Seismic Design Guidelines for Dikes - 2nd Edition

Transcription

Seismic Design Guidelines for Dikes
2nd Edition
Dike Embankment Failure at Capitol Lake
Nisqually Earthquake, February 2001
Hanshin Earthquake, 1995
Ministry of Forests, Lands and Natural Resource Operations
Flood Safety Section
June 2014
SEISMIC DESIGN GUIDELINES FOR DIKES
2nd Edition
Prepared For
Ministry of Forests, Lands and Natural Resource Operations
Flood Safety Section
By
Upul Atukorala, Ph.D., P. Eng.
Herb Hawson, P. Eng.
Brian Mylleville, Ph.D., P. Eng.
Randy Williams, P. Eng.
June 2014
CONTENTS
1. Preamble .................................................................................................................................. 1 3. Application .............................................................................................................................. 2 4. Background ............................................................................................................................. 3 5. Discussion and Application of Guidelines to Highly Vulnerable Sites .............................. 4 6. Disclaimer ................................................................................................................................ 5 7. Definitions ............................................................................................................................... 5 8. Design Objectives ................................................................................................................... 6 9. Seismic Hazards Considered ................................................................................................. 7 10. Water Levels and Post-Earthquake Freeboard .................................................................. 7 11. Information to be Accessed and Reviewed ........................................................................ 8 12. Geotechnical Investigations for Seismic Design ............................................................... 9 13. Performance-Based Seismic Design Criteria ................................................................... 11 14. Selection of Time-Histories ................................................................................................ 12 15. Analysis Methods ............................................................................................................... 13 16. Dike Remediation Methods ................................................................................................ 24 17. Threshold Seismic Event for Post-Event Dike Integrity Inspection ............................... 25 18. Post-Earthquake Emergency Repair of Dikes .................................................................. 28 19. References........................................................................................................................... 28 List of Tables
Table 1: Return Periods and Annual Exceedance Probabilities ................................................ 7 Table 2: Summary of Maximum Allowable Dike Crest Displacement Corresponding to
Performance Categories ........................................................................................... 12 Table 3: Amplification of Ground Motions – Level Ground ...................................................... 15 Table 4: Modification Factors to Account for Topographic Effects .......................................... 15 Table 5: Analysis Methodologies for Varying Liquefaction Indices ......................................... 16 Table 6: Earthquake Magnitude- Epicenter Distance Pairs for Dike Inspection ...................... 26 Table 7: Modified Mercalli Intensity Scale Correlated to Damage Potential and Peak Ground
Acceleration............................................................................................................... 27 Page i
List of Figures
Figure 1: Dike Locations in the Fraser Valley
Figure 2: Empirical Liquefaction Resistance Charts When Using SPT (Mw =7.5)
(Youd et al, 2001)
Figure 3: Empirical Liquefaction Resistance Charts When Using CPT (Mw =7.5)
(Youd et al, 2001)
Figure 4: Topographic Amplification (Faccioli, 1991).
Figure 5: Liquefaction Susceptibility
Figure 6a: Residual Shear Strength Ratio of Soils vs SPT Resistance
(Idriss & Boulanger, 2008).
Figure 6b: Residual Shear Strength Ratio of Soils vs CPT Resistance
(Idriss & Boulanger, 2008)
Figure 7a: Volumetric Strain of Soils vs SPT Resistance (Mw =7.5) (Idriss & Boulanger, 2008)
Figure 7b: Volumetric Strain of Soils vs CPT Resistance (Mw =7.5) (Idriss & Boulanger, 2008)
Figure 8a: Data Collection and Evaluation of Liquefaction Index
Figure 8b: Typical Analysis Flow Chart for Liquefaction Indices L0/L1
Figure 8c: Typical Analysis Flow Chart for Liquefaction Index L2
Figure 8d: Typical Analysis Flowchart for Liquefaction Index L3
Figure 9: Distance from the Fault to Farthest Liquefaction Observed vs Earthquake Magnitude
(Youd, 1991)
Figure 10: Distance from Earthquake Epicenter vs Earthquake Magnitude Causing Damage to
Earth Structures (Tani, 1996)
Figure 11: Correlation of Moment Magnitude with other Magnitude Scales (Youd & Idriss, 1997)
List of Appendices
APPENDIX A Literature Review of Seismic Design Guidelines for Flood Protection Dikes APPENDIX B Earthquake Inspection Checklist APPENDIX C Failure Mechanics and Ground Treatment Methods APPENDIX D Remediation of Seismic Damage to Dikes APPENDIX E Report Format/Table of Contents Seismic Design and Analysis Requirements for Dikes APPENDIX F Example Problem – Dike Seismic Stability Page ii
1. Preamble
The purpose of this document is to provide guidelines for consideration of
seismic stability and integrity of the High Consequence Dikes in Southwestern
British Columbia and Vancouver Island with the intent to provide flood
protection for the densely populated urban communities and regional
infrastructure. Guidelines are provided on:






Seismic ground motions to be considered for the analysis and design of
dikes along with corresponding performance expectations;
Suitable geotechnical investigation methods to characterize and obtain
engineering properties of the site soils;
Commonly used methods for seismic analysis considered appropriate for
dikes;
Seismic rehabilitation and strengthening measures;
Threshold seismic events that should trigger a post-event evaluation of
the integrity of the dike system; and
Post-earthquake temporary emergency repair and permanent
remediation measures.
The west coast of British Columbia, including Vancouver Island, is a region of
high seismic hazard in Canada. The seismic hazard is caused by the Juan
de Fuca Plate subducting under the North American Plate resulting in large
earthquakes of magnitude varying from Mw6 up to Mw9.
Densely populated urban communities and regional infrastructure in British
Columbia are protected from flooding by some 300 km of river and sea dikes.
The original dikes constructed in the early years were levees built with local
fills and to very rudimentary standards. These dikes were upgraded in the
1970s and 1980s to design standards that existed at that time. During these
upgrading works, the potential for earthquake-induced soil liquefaction and
associated potential for damage was reviewed, but the cost to design for
seismic loading was not judged to be commensurate with the consequences
to the community.
Since that time, municipalities throughout the
Lower Mainland have seen extensive population growth and the
consequences to the communities and infrastructure has increased. The
extent of damage resulting from large scale flooding resulting from breaches
to the different diking systems has been estimated to reach upwards of
$50 Bn (2013 dollars).
Flood protection dikes are almost always located along river banks and
shorelines that have historically experienced considerable damage following
earthquakes. Therefore, dikes have a high geo-hazard exposure and need to
be investigated in detail to allow identification and assessment of soil strata
that are vulnerable to liquefaction, loss of shear strength, and displacement
during seismic design.
This guideline has adopted a combination of traditional and
performance-based design criteria for the seismic design of dikes. Dike
performance is specified in terms of measureable criteria such as crest
displacements of the dike structure. The methodologies and criteria provided
in the document were established following a review of practices currently
followed in other regions of the world that are also prone to high seismic
hazards.
Page 1
The maximum allowable displacements have been established with the
intent of preserving the structural integrity of the dike body. It is implied
that by conducting field investigations and displacement analyses at sections
that are separated by a horizontal distance less than 300 m and satisfying the
maximum allowable dike crest displacements prescribed in this guideline
would reduce the potential of a dike breach as a result of differential or
relative displacements.
It is acknowledged that achieving the dike performance criteria specified in
this document may be difficult and costly in some instances considering that a
majority of the dikes have originally been built to rudimentary standards. It is
also recognized that the flood protection offered by the diking system is
dependent on the performance of the weakest areas of the specific diking
system. After the seismic assessment has been completed it may be
necessary for the Diking Authority to consider, with backup analyses, possible
alternatives such as dike realignment in areas of high seismic vulnerability,
overbuilding the dike, incorporating the dike into adjacent land development
areas, and restricting land use and regulating floodplain development to arrive
at practical and cost-effective remedial measures.
The guidelines have been developed with the intent of achieving a
consistently uniform assessment of the dike integrity and performance under
seismic loading conditions by the different practitioners. Prescriptive seismic
loading criteria and analysis methods including reporting requirements are
identified, where feasible, to achieve this objective.
“Mean annual sea water levels” and “mean annual river water levels” are
judged as appropriate to be used in the dike seismic integrity assessment
with regards to seismic stability and displacement calculations, rather than
water levels established based on probabilistic methods. For some urban
communities, varying water levels including the projected rise in sea levels
and higher levels of free-board are to be considered to provide an appropriate
level of protection.
There are only a few countries in the world where extensive population is
protected by flood control dikes located in areas of high seismicity, and in
some ways British Columbia is unique in this respect. In the event of dike
failure under flood conditions, extensive infrastructure and environmental
damage as well as social disruption to communities should be expected.
Seismic design may impact dike alignment and land acquisition requirements,
and it is recommended that pre-feasibility geotechnical studies, including the
seismic assessments, be completed prior to detailed civil design of the dike.
The locations of most of the dike systems under consideration of these
guidelines are shown on Figure 1.
3. Application
These guidelines apply to the design and construction of new and major
upgrades to High Consequence Dikes. Seismic assessments and designs
must generally be consistent with these guidelines to obtain
Dike Maintenance Act approval from the Ministry prior to construction (also
see “Discussion of Application of Guidelines for Highly Vulnerable Sites”
below).
Page 2
4. Background
This is the second edition of the “Seismic Design Guidelines for Dikes” which
were first published in August, 2011. The following section briefly reviews the
history and rationale for seismic guideline development for dikes.
The west coast of British Columbia including Vancouver Island is an
earthquake prone region because of the tectonic setting and movements at
plate boundaries. The Lower Mainland is a high seismic hazard region where
there is potential for extensive earthquake damage to the Fraser River and
sea diking systems that protect dense urban areas and critical regional
infrastructure. Seismic hazard is generally lower in the British Columbia
interior due to the reduced intensity of shaking and because there are fewer
High Consequence Dikes.
The 1968 to 1994 Fraser River Flood Control Program (FRFCP)
reconstructed approximately 300 km of river and sea dikes to a hydraulic
standard of approximately 1:200 annual exceedance probability. Except for
the major Barrowtown Pump Station in Abbotsford, the FRFCP design criteria
(developed over 40 years ago) did not address seismic design issues largely
because of cost constraints. This approach was rationalized on the basis of
the rare chance of occurrence of a major flood simultaneously with a large
earthquake. In the 1970’s it was also anticipated that development of
upstream storage reservoirs in the Fraser River watershed would significantly
reduce the Fraser River flood threat and justify a relatively modest standard of
dike protection.
Extensive urban development in the floodplain over the past several decades
has increased reliance on the diking systems and significantly increased the
consequences associated with poor performance of the diking system.
Comprehensive hydraulic modeling and better understanding of sea level rise
has resulted in higher design flood levels. In consideration of increasing sea
level rise related flood hazard and urban development related consequences,
the Ministry initiated development of design guidelines to explicitly address
the seismic hazard aspects of dike design.
In November 2010, interim guidelines were issued that required the design of
dikes to consider the effects of seismic activity on the integrity of the dike
structure and required the owner to demonstrate that it would be possible to
re-construct the dike within 6 months of the earthquake to retain a 1:10 yr
annual exceedance probability flood.
This approach had the benefit of assessing potential damage, however, the
feasibility of repair and re-construction was difficult to demonstrate. While
rapid re-construction may be feasible for discrete, short sections of dike,
re-construction to address widespread damage throughout the diking system
may be difficult when dike work would be competing for resources for
re-construction of other critical infrastructure such as water supply, sewer,
roads and bridges. If the dikes cannot be repaired promptly, large sections of
communities in low lying areas would be vulnerable to flooding, even from low
return period events.
To address these issues, the Ministry published new guidelines in
August 2011 (the first edition of these guidelines) that specified a level of
required dike performance in terms of vertical and lateral dike deformation in
response to three different levels of earthquake shaking or ground motions.
Page 3
A review of the published seismic design requirements established for dikes
and levees in other jurisdictions has been undertaken to provide insight on
seismic design guidelines “currently” adopted by the profession. The reader
is referred to Appendix A for details. The following summarizes the broad
trends in the overall analysis procedures:
1. In general, dikes are designed using low hazard probabilities when
considering high consequence circumstances. Historically, this has been
achieved implicitly through traditional design criteria by prescribing factors
of safety against failure and considering conservatively estimated loads
and capacities. These traditional design criteria have evolved over time to
achieve acceptable risks.
2. More recently, seismic design of dikes has evolved to include
performance-based design criteria considering more than one level of
ground shaking and by specifying the acceptable performance for each
level of shaking.
3. Another more comprehensive approach that has evolved, but is at the
initial stages, is the design of earth structures such as dams through risk
assessment and management by specifying the probability of types of
failure or reliability of particular components with respect to various
functions. This latter approach involves an assessment of the societal
risk and considers many other factors such as loss of life, impact to the
environment and cultural values, and impact to infrastructure and
economics.
This guideline has adopted a combination of traditional and
performance-based design criteria for the seismic design of dikes. The
required performance of dikes is specified in terms of measureable criteria
such as displacements within the dike structure as a result of design seismic
loading. Satisfactory dike performance is implicitly taken into consideration
by specifying multiple levels of earthquake shaking or ground motions and
corresponding performance expectations that can be varied to achieve a high
or low degree of safety/reliability.
These guidelines are not intended to explicitly consider probability of dike
failure and/or level of post-earthquake flood protection. Consideration of
combined probabilities and level of post-earthquake flood hazard protection
must be developed on a regional dike network level basis, which is outside
the scope of the current guidelines. A regional dike network level risk
framework is under consideration for the Fraser River in the Lower Mainland
and Fraser Valley by the Fraser Basin Council.
5. Discussion
and
Application of
Guidelines to
Highly
Vulnerable
Sites
Seismic strengthening and dike remediation methods are covered later in
these guidelines (Section 16.) and in Appendix C. Ground improvement
methods are costly and may only be practical for short sections of dike and
appurtenant structures. After the seismic assessment has been completed it
may be necessary for the Diking Authority to consider the following possible
alternatives in situations where the displacement criteria cannot be met:

Re-aligning the dike to avoid the high cost of ground improvement where
the dike is located in seismically vulnerable areas adjacent to steeply
sloping river banks.

Overbuilding the dike to satisfy post-earthquake vertical displacement
requirements provided that displacement analyses confirm that the dike
Page 4
core will retain hydraulic integrity and the landside face geometry remains
intact (i.e. “modifying the dike profile” as discussed on
Section 16.).

Incorporating the “dike” into massive fills required for adjacent land
development (i.e. the “superdike” concept) again with sufficient analyses
to confirm that the flood protection system would retain its hydraulic
integrity.

Documenting expected damage, putting together a remediation plan,
restricting land use and regulating floodplain development in the protected
area (e.g., flood proofing bylaws and other regulatory tools) to justify
removal of the High Consequence Dike classification.
Because seismic design may impact dike alignment and land acquisition
requirements, it is a general recommendation that pre-feasibility geotechnical
studies, including the seismic assessment, should be completed prior to
detailed civil design of the dike.
6. Disclaimer
This document provides a set of guidelines (requirements) for the seismic
design of High Consequence Dikes. Golder is the sole author of this
document with input and direction from the Ministry of Forests Lands and
Natural Resource Operations and review and input by Thurber Engineering
Ltd. It is expected that the guidelines may be further expanded and/or
modified in response to feedback from the Ministry and other stakeholders.
Designers must use their own judgment in interpreting and applying the
guidelines contained in this document and take full responsibility for the
designs proposed. Golder Associates Ltd. and the Ministry of Forests Lands
and Natural Resource Operations do not guarantee and are not responsible
for the content, accuracy and completeness of the guidelines and accept no
responsibility for the use of these guidelines. Designers’ use of the guidelines
is at their sole risk and liability.
7. Definitions
Dike: In the Dike Maintenance Act, a “dike” is defined as an embankment,
wall, fill, piling, pump, gate, floodbox, pipe, sluice, culvert, canal, ditch, drain
or any other thing that is constructed, assembled or installed to prevent the
flooding of land. For purposes of this guideline, the definition has been
simplified to represent a manmade barrier constructed of soil and/or structural
elements (such as floodwalls) along a water course for the primary purpose of
providing flood protection.
High Consequence Dikes: flood protection dikes where the economic and/or
life safety consequences of failure during a major flood are very high. These
dikes typically protect urban or urbanizing areas, and failure could result in
large economic losses and/or significant loss of life. The majority of the dikes
reconstructed under the 1968 to 1994 Fraser River Flood Control Program
would be considered High Consequence Dikes.
Floodwall: a manmade barrier constructed of material other than soil along a
water course for the primary purpose of providing flood protection.
Liquefaction: describes a phenomenon whereby a saturated soil loses
significant portion of strength and stiffness in response to a sudden change in
stress and/or pore pressure condition which causes the soil to behave like a
viscous fluid.
Page 5
Liquefaction Susceptibility: is a reference to the ability of the soil deposit to
liquefy when subjected to an applied stress. For example, a dry or
unsaturated granular deposit does not have the ability to liquefy due to the
absence of saturated conditions. Cohesive deposits are also not susceptible
due to the particle structure of the deposits and the interstitial forces that hold
the clay molecules together (cohesion).
Liquefaction Potential: is a reference to the resistance of a deposit to
liquefaction as a result of a sudden change in stress level and/or pore
pressure condition due to cyclic loading.
Cyclic Mobility: refers to cumulative displacements that occur during each
cycle of shear stress due to softening (without liquefaction) and the
displacements are generally significantly less than liquefaction-induced
displacements.
Flow Slide: significant translational type displacement of a land mass when
static shear stresses exceed the undrained residual shear strength of
liquefied soil (i.e., a factor of safety against slope failure equal to or less than
1.0 when using liquefied soil strengths and no inertial loads).
Bearing Capacity: the ability of a deposit to support an external load without
developing a soil shear failure (i.e., plastic flow and/or a lateral expulsion of a
soil from beneath the applied load).
Moment Magnitude: is a measure of the amount of energy released during an
earthquake which is not dependent on ground shaking levels or level of
damage (i.e., Wood & Neumann (1931)), but reflects factors that are
characteristic to the rupture of the fault that produces the earthquake.
Return Period: a reference to the frequency or return time period for a
specific seismic hazard (i.e., 1 in 2,475 yr). The seismic hazard is normally
expressed as a percent chance of exceedance over a specified period of time
(i.e., a 2% chance of exceedance in 50 years). Another form of expressing
the seismic hazard is in terms of probability of exceedance which considers
the probability that an earthquake will generate a level of ground motion that
exceeds a specified reference level during a given exposure time.
Piping Failure: piping occurs when hydraulic gradients at or near the ground
surface or free face exceeds unity (i.e., the change in total head pressure
head over a unit path length exceeds unity). Over a prolonged period of time,
internal erosion can generate an “effective” pipe condition leading to
increased flow and eventual collapse of the soil deposits.
8. Design
Objectives
The design objectives for dikes are established as follows:



Dikes subjected to seismic ground motions with a short return period or a
high annual exceedance probability event during the design life should
perform with insignificant damage to the dike body, without compromising
the post-earthquake flood protection ability;
Dikes subjected to seismic ground motions with an intermediate return
period or an intermediate annual exceedance probability event during the
design life may experience some repairable damage to the dike body,
without compromising the post-earthquake flood protection ability; and
Dikes subjected to seismic ground motions with a long return period or a
rare or a low annual exceedance probability event during the design life
Page 6
may undergo significant damage to the dike body potentially requiring
more complex subsurface repairs, with the short-term post-earthquake
flood protection ability possibly compromised.
Refer to Section 13(2) for performance categories with respect to
displacements and anticipated damage.
Typical return periods or annual exceedance probabilities considered are
summarized in Table 1:
Table 1: Return Periods and Annual Exceedance Probabilities
9. Seismic
Hazards
Considered
Percent
Chance of
Being
Exceeded in
100 Years
Return Period
Classification
Event
Classification
Return Period
(Years)
Annual
Exceedance
Probability
Short
Frequent
100 to 200
0.01 to 0.005
65% to 40%
Intermediate
Intermediate
475 to 975
0.0021 to 0.001
20% to 10%
Long
Rare
2,475 to
10,000
0.0004 to 0.0001
4% to 1%
Potential seismic hazards affecting the dikes located in Southwestern British
Columbia include the following:

Ground shaking;

Slope displacements caused by ground shaking;

Bearing capacity and sliding failure;

Soil liquefaction;

Vertical and horizontal total and differential ground displacements;

Loss of free board due to ground subsidence and slope failure; and

Piping failure through fissures induced by ground displacements.
The seismic hazard to Southwestern British Columbia results from the
offshore subducting of the Juan de Fuca Plate beneath the Continental Plate.
The tectonic environment gives rise to three different types of earthquakes,
each with its own specific characteristics; i.e., shallow crustal earthquakes (up
to Mw7.5, with epicenter as close as a few km from the site of interest), deep
intra-plate earthquakes (up to Mw7.5, with epicenter as close as 40 km from
the site of interest), and inter-plate or subduction earthquakes (up to
Mw9, with epicenter as close as about 140 km from the site of interest).
10. Water
Levels and
PostEarthquake
Freeboard
Spring snowmelt freshets pose the main flood hazard for the Lower Fraser
River flood plain areas. Flooding that results from heavy rainfall in the fall and
winter is also a significant concern for the diked reaches of coastal rivers.
High tides can impact a sea dike at any time of the year, and storm surge
events are most frequent during the fall and winter period. The flood hazards
resulting from channel obstructions due to ice jam formations are considered
to be possible, but less likely, particularly in Southwestern BC. Combining the
peak water levels that occur annually over a short period with rare earthquake
ground shaking for use in a dike stability/displacement analysis, is generally
considered to result in overly conservative designs.
Page 7
In order to avoid unrealistically low combined probabilities, “mean annual river
water level” and “mean annual sea water levels” should generally be used in
the stability and displacement calculations completed as part of the seismic
assessment of dikes. However, in some instances (e.g. for sea dikes
exposed daily to both high and low tides), the sensitivity of the stability and
displacement calculations to varying water levels should be considered.
Future dike upgrades may need to consider projected rise in sea levels.
The designers should refer to the Ministry of Environment,
Water Management Branch report entitled, Climate Change Adaptation
Guidelines of Sea Dikes and Coastal Flood Hazard Land Use (3 Volumes),
dated January 2011.
Vertical displacement will reduce the available post-earthquake free
board relative to the design flood level. However, the loss of free board is
not as critical as the integrity of the diking system to protect against the
occurrence of smaller floods during a possibly extended period (i.e., several
months to a few years) before the damaged sections can be fully restored to
their design condition.
The Performance Categories and Permissible Displacements provided later in
these guidelines are intended to limit the damage and retain
post-earthquake flood protection capability for at least the 1:100-yr and
1:475-yr return period ground motions with some compromised flood
protection for the 1:2,475-yr return period ground motions (See Table 2).
11.
Information to
be Accessed
and Reviewed
Dikes may be constructed, rehabilitated, or altered in segments, however, the
seismic stability of the entire dike should be addressed. As a minimum, the
following information should be collected, compiled, and reviewed prior to and
during construction, rehabilitation, and alteration of dikes:
1. Available drawings showing the dike cross section, materials used for
construction, construction details such as level of compaction for the dike
segments of concern and adjoining segments, drawings and design
details for appurtenant structures such as flood boxes and pump stations;
2. Dike inspection reports summarizing past performance of the dike
segment;
3. Available geotechnical borings, reports, and as-built (record) drawings
prepared and completed by engineers and contractors during initial dike
construction and subsequent modifications/alterations (if applicable);
4. Data on mean river water and mean ocean water levels;
4. Ground shaking levels for return periods of 100-yr, 475-yr, and 2,475-yr
by establishing the UTM coordinates for the site and from the Natural
Resources Canada website
http://earthquakescanada.nrcan.gc.ca/hazard-alea/interpolat/index_2010eng.php
5. Topographic and Bathymetric data for the area adjacent to the dikes. The
geometric data should extend a sufficient distance beyond the dike
(upstream and downstream) to support static, hydrostatic and dynamic
analyses of the dike structure, particularly where performance criteria are
considered for establishing a seismic design basis for the dikes.
Bathymetry data collected within the last 2 years is preferable. A detailed
discussion is required to demonstrate the appropriateness of the
topographic and bathymetric data used in the analysis; and
Page 8
6. Surficial geology maps and aerial photographs.
It should be recognized that the ground surface accelerations experienced by
the dike structure during a seismic event at any given site will be influenced
by the underlying ground conditions. Amplification or de-amplification of firm
ground accelerations may occur but will depend on the site-specific ground
conditions and should be considered in design.
12.
Geotechnical
Investigations
for Seismic
Design
Flood protection dikes are almost always located along river banks and
shorelines.
Historically, river banks and shorelines have experienced
considerable damage following earthquakes due to soil liquefaction, slope
failure, settlement, and permanent lateral displacement. As a result, dikes
have a high geo-hazard exposure and need to be investigated in detail to
allow identification and assessment of soil conditions and strata that are
vulnerable to liquefaction, loss of shear strength, and displacement.
The main objective of the geotechnical investigation is to identify soil strata
that are susceptible to liquefaction and/or cyclic softening as a result of strong
ground shaking, to determine their in-situ state and engineering properties. A
suitable investigation should include, but may not be limited to, the following:

Continuous or near-continuous profiles of the soil strata;

Measurement of depth to ground water levels on either side of and within
the dike;

In-situ testing of soil strata susceptible to liquefaction and/or cyclic
mobility in the form of penetration resistance, strength, and shear wave
velocity;

Sampling of soil strata susceptible to liquefaction and/or cyclic mobility;

Gradation of soils susceptible to liquefaction and/or cyclic mobility;

Index testing of soils susceptible to liquefaction and/or cyclic mobility; and

Cyclic simple shear testing of fine-grained soils to investigate liquefaction
susceptibility and/or cyclic mobility.
Dikes comprise hundreds of kilometres of earth fill embankments constructed
over varying ground conditions that may include reclaimed areas, buried
channels, previous failures, river meander and bar deposits, and
marshy/swampy areas. The flood protection offered by the dike system is
dependent on the performance of the weakest areas of the specific dike
system, and this aspect should be taken into consideration when planning
field investigations.
Several different field investigation methods are commonly used by
practitioners to obtain engineering properties of soils. These include the
Standard Penetration Test (SPT), the Cone Penetration Test (CPT), Becker
Penetration Test (BPT), and Shear Wave Velocity Test (SWVT) methods:

SPT Method: This is the most common field investigation method used
to identify soils that are susceptible to liquefaction. It has the advantage
that a disturbed sample is recovered after each test at set intervals of
generally 1 to 2 m. This procedure has strict requirements for hammer
energy, sampler size, and drilling method. Performing SPTs in gravelly
soils require special consideration due to the coarse size of soil particles
Page 9
and the resulting misleadingly high blow count data. The method is
operator dependent and should be carried out in accordance with current
ASTM standards. The results should be carefully interpreted and
corrected according to established procedures. SPT sampling is not
considered appropriate for use in coarser granular soils containing
significant gravel and larger particle sizes.

CPT Method: For many sites, the CPT is the preferred method to identify
soils that are susceptible to liquefaction. The method provides a nearcontinuous indication of soil consistency and type with depth, and is less
susceptible to operator-related differences in measurements; however,
testing should be carried out in accordance with current ASTM standards.
The method is capable of detecting relatively thin layers of soil. The cone
results should be correlated with data from nearby borings, where local
correlations do not exist. The method does not provide soil samples and
is not suitable for use in soil strata containing significant gravel and larger
particle sizes or highly consolidated deposits (i.e., glacial till).

BPT Method: This is the preferred method of field investigation for sites
underlain by coarse-grained soils (i.e., gravel and cobbles) that are
susceptible to liquefaction. Reliable data can be obtained provided that
accurate bounce chamber pressure or hammer energy measurements are
carried out and industry established and accepted procedures for data
reduction and interpretation are followed.

SWVT Method: Shear wave velocity is the primary parameter used for
Site Classification as per 2010 National Building Code of Canada (NBCC)
and other current standards and codes. The data is used for the
determination of soil shear moduli for ground response analysis.
Experienced individuals should perform these tests, as the collection of
results requires considerable skill and expertise.
Other field exploration and in-situ testing methods for assessment of soil
liquefaction may be used with site-specific correlations with one of the
methods described above.
In addition, soil sampling using sonic drilling methods may provide important
information on the soil layering in some projects. Sonic drilling is able to
provide continuous sampling to assist with identifying transition zones
between strata as well as provide the opportunity for bulk sampling.
Generally, the method does not provide a means to develop engineering
properties of the deposits.
All field investigations should be undertaken in accordance with published
standards, where applicable.
The field investigations should include test holes that extend to depths
between about 10 m and 30 m below existing ground surface or to practical
refusal to further penetration, whichever occurs first.
A minimum of three borings should be considered for each section of the
dike; one on the water side of the dike, one through the center of the dike,
and one on the land side of the dike. The horizontal spacing of data sections
along the dike should not be greater than 300 m. Closer spacing of data
sections may be required where significant variations in subsurface conditions
are anticipated.
Page 10
For dike segments where the available subsurface data is limited, the initial
analyses and investigations may be carried out in stages, starting with
screening level analyses/investigations. However, the final design and
analysis of the dike segment should incorporate subsurface investigations as
identified above.
13.
PerformanceBased Seismic
Design
Criteria
A performance-based seismic design is accomplished by defining appropriate
levels of design earthquake ground motions and corresponding acceptable
levels of damage. The design earthquake motions include those from
frequent events that are likely to occur within the life of the structure as well
as infrequent or rare events that typically involve very strong ground shaking.
The acceptable level of damage is specified in terms of displacements to be
experienced by the structure.
Damage is categorized in terms of
“Performance Categories”, which are related to the effort required to restore
the full functionality of the structure. The performance of the dike system
should be checked for all three Design Earthquake Ground Motion
Levels defined below:
1. Design Earthquake Ground Motions
Ground motions that correspond to three different return periods
described below shall be considered in seismic design.

Earthquake Shaking Level 1 (EQL-1)
1:100-yr return period ground motions that are equivalent to having a
40% chance of exceedance in 50 years or 63% chance of
exceedance in 100 years.
For dikes located in the Lower Mainland, this level of shaking is
associated with an Mw6 earthquake.

10% chance of exceedance in 50 years or 19% chance of
exceedance in 100 years.

2% chance of exceedance in 50 years or 4% chance of exceedance in
100 years.
2. Performance Categories and Permissible Displacements
Performance Category A: No significant damage to the dike body, post
seismic flood protection ability is not compromised.
Performance Category B: Some repairable damage to the dike body,
post-seismic flood protection ability is not compromised.
Performance Category C: Significant damage to the dike body,
post-seismic flood protection ability is possibly compromised.
Page 11
Table 2: Summary of Maximum Allowable Dike Crest Displacement
Corresponding to Performance Categories
Performance
Category
Earthquake
Shaking Level
Maximum Allowable
Vertical
Displacement
Maximum Allowable
Horizontal
Displacement
A
EQL-1
small (<0.03 m)
small (< 0.03 m)
B
EQL-2
0.15 m
0.3 m
C
EQL-3
0.5 m
0.9 m
The maximum allowable displacements given in Table 2 have been
established with the intent of preserving the structural integrity of the dike
body. They represent total displacements. It is implied that for earthen dikes,
satisfying the maximum allowable dike crest displacements at sections that
are located with a maximum horizontal distance of 300 m along the dike
would reduce the hazards associated with a dike breach as a result of
differential or relative displacements.
It should be recognized that the design of structural elements such as
floodwalls may need to satisfy alternate (less tolerant) displacement
criteria in order to achieve the performance expectations described
herein.
The designer shall independently confirm that the displaced configuration of
the diking system would provide at least 0.3 m of post-earthquake freeboard
above 1:10-yr return period water level to meet performance expectations.
Individual communities that are assessed as having high economic loss and
damage to environment as a result of flooding may impose more stringent
minimum post-earthquake freeboard than specified herein.
14. Selection
of TimeHistories

Time-histories selected for Newmark or dynamic analysis of the dike
system should be from a seismo-tectonic & geologic settings comparable
to those relevant to the site of interest.

The time-histories selected for Newmark or dynamic analysis should be
consistent with the magnitude/distance/duration scenario developed for
the analyses.

Linear scaling or time domain spectral matching are the preferred
approaches to matching a time-history to a target response spectrum over
the period range of interest.

Multiple time-histories should always be used in dynamic analyses.
Typical practice considers the maximum response of three (3)
time-histories or an average response of seven (7) or more
time-histories. When selecting three (3) time-histories, they should
correspond to three different historical earthquakes.
Unless otherwise approved by the Diking Authority, the seed ground motions
obtained from the following two websites shall be used with uniform and linear
scaling to match the site-specific peak firm-ground horizontal acceleration in
dynamic analysis of dikes:
a) http://peer.berkeley.edu/peer_ground_motion_database/
b) http://strongmotioncenter.org/
Page 12
15. Analysis
Methods
The assessment of seismic hazards on dikes involves several steps:
Step-1:
Evaluate applicable ground surface acceleration, crest
acceleration, and accelerations at selected locations of the dike;
Step-2:
Evaluate liquefaction
consequences;
Step-3:
Evaluate stability of slopes under seismic loads, including postearthquake flow-slide failure;
Step-4:
Evaluate seismic displacements; and
Step-5:
Evaluate post-event piping failure potential.
potential
of
soil
and
associated
Steps-1 through-4 may be carried out using either simplified
(i.e., Newmark) or finite difference/finite element methods of analyses, as the
situation may warrant, with the realization that simplified methods provide
limited information in comparison to rigorous methods. Step-5 involves an
assessment of post-event field inspection observations and does not require
specific analyses.
In design, soil-structure interaction analysis may need to be carried out to
address relative displacements (and performance) of appurtenant structures
such as flood boxes and pump stations and the adjacent earthen dike
structure. Appurtenant structures may also include residential/commercial
developments built into the dike body where consideration of seismic earth
pressures affecting the seismic performance of any below grade walls must
be explicitly considered, particularly the potential for cracking of concrete.
It should be recognized that during earthquake shaking, the earthen dike
mass may or may not move relative to the adjacent more rigid appurtenant
structure(s) depending on the ground conditions and foundation elements that
support appurtenant structures. In situations where relative displacements
are expected to occur between the appurtenant structure(s) and the adjacent
earthen dike mass, appropriate design elements (e.g., flexible wing walls,
“water stops” or similar technology) should be incorporated to prevent
leakage/soil loss at these interfaces. A description of the proposed details
and anticipated performance of appurtenant structures should be provided for
review by the Deputy Inspector of Dikes under the Dike Maintenance Act and
by the Diking Authority.
Guidelines on the appropriate methods of analyses for Steps-1 through 4 are
provided below:
EQL-1 (100-yr Return Period):
Slope stability based on pseudo-static analysis method.
based on Newmark analysis method.
Displacements
EQL-2 & EQL-3 (475-yr Return Period and 1:2475-yr Return Period):
The types of analyses required are dependent on the Liquefaction Index, Li,
established based on Seed’s Simplified Method of Analysis (SSMA) and the
empirical liquefaction resistance charts shown in Figures 2 and 3.
Li is defined as follows:
L0:
No liquefaction,
(Ru ≤ 20%);
no significant excess
pore
water
pressures
Page 13
L1:
Complete liquefaction not expected (i.e., FOSliq > 1.2), limited excess
pore water pressures (Ru ≤ 50%);
L2:
Liquefaction occurs in zones of limited thickness; and
L3:
Complete liquefaction of soils.
Figure 2: Empirical Liquefaction Resistance Charts When Using SPT (Mw = 7.5)
(Youd et al, 2001).
Figure 3: Empirical Liquefaction Resistance Charts When Using CPT (Mw = 7.5)
(Youd et al, 2001).
Fine-grained silty soils that exhibit plasticity indices [PI] less or equal to 7,
should be treated as granular soils with appropriate corrections to penetration
resistance based on fines content.
Page 14
Fine-grained soils with PI values in excess of 7 are unlikely to undergo
liquefaction and substantial softening during cyclic loading and should be
treated as clayey soils with undrained shear strength consistent with field and
laboratory measurements.
The ground motion amplification factors given in Table 3 as a function of the
Site Class and Table 4 may be used in the SSMA to compute the peak
ground surface acceleration, as per Table 4.5.1.9 of NBCC 2010.
Alternatively, they may be derived or inferred from site-specific ground
response analyses carried out using wave propagation methods. The peak
horizontal ground surface accelerations used in the SSMA shall be the larger
of the values computed from site-specific wave propagation analyses or,

80% of the PGA derived from the amplification values given in Tables 3
and 4 when combined with Class C PGA for EQL-1


The amplification factors given in Table 3 are applicable for level ground
conditions. For convex surfaces such as dikes, the crest amplifications may
be established as the product of the firm-ground acceleration, amplification at
level ground (Ampllevel-ground) and a modification factor Amplapex to account for
the apex angle of the dike (see Figure 4 for definition of apex angle and
suggested amplification factors.
Topographical amplification factors
established by other published data sources are also acceptable:
[1]
PGAcrest = PGAfirm-ground x Ampllevel-ground x Amplapex
Table 3: Amplification of Ground Motions – Level Ground
Site
Classification
Amplification - Level Ground Conditions (Ampllevel-ground)
Sa (0.2) ≤
0.25
Sa (0.2) =
0.50
Sa (0.2) =
0.75
Sa (0.2) =
1.00
Sa (0.2) ≥
1.25
Soil Class E
2.1
1.4
1.1
0.9
0.9
Soil Class D
1.3
1.2
1.1
1.1
1.0
Soil Class C
1.0
1.0
1.0
1.0
1.0
Soil Class B
0.8
0.8
0.9
1.0
1.0
Table 4: Modification Factors to Account for Topographic Effects
Apex Angle (φ2)
Modification Factor
(Amplapex = A2/A1)
1800
1.0
0
1.1
0
1.2
0
1.3
165
150
140
Page 15
Figure 4: Topographic Amplification (Faccioli, 1991).
Table 5: Analysis Methodologies for Varying Liquefaction Indices
Liquefaction
Index
Slope Stability
Displacements
Insignificant (L0)
Pseudo-Static
Newmark1
Mild (L1)
Pseudo-Static
(Reduced Shear Strength)
Newmark1
(Reduced Shear Strength)
Moderate (L2)
Pseudo-Static
(Residual/Liquefied Shear
Strength)
Newmark
Finite Difference/Finite Element Numerical
Models
(Suitable Soil Models to Account for NonLinear Strength Reduction Under Cyclic
Loading)
High (L3)
Pseudo-Static
(Residual/Liquefied Shear
Strength)
Pseudo-Static (Remediated
Case)
Newmark (Unremediated Case
Residual/Liquefied Shear Strength)1
Newmark (Remediated Case, Without
Optimization)1
Finite Difference/Finite Element Numerical
Models
1
1
The well-established Newmark sliding block method of analysis, when used with
appropriate soil properties, is considered as the preferred method of estimating seismic
displacements compared to other empirical methods. For consistency and uniformity in
assessment of displacements by Practioners, only this method of analysis will be accepted
by the Provincial Flood Safety Section for analysis scenarios outlined in Table 5. Other
(rigorous) methods of displacement calculations may be more suited and should be used,
at the discretion of the practitioner, when predicting more accurate magnitude and pattern
of displacements are required.
Reduced Strength for the Liquefaction Indices of L0 and L1 should be
determined based on the anticipated excess pore water pressures developed
in the different dike zones due to ground shaking and should be a maximum
of 80% of the drained strength of each respective zone.
Page 16
Dike slope stability and displacement analyses shall consider both circular
and non-circular slip surfaces as appropriate for the site-specific soil
stratigraphy. The critical slip surface that corresponds to static stability shall
be determined first. The magnitude of seismic displacements estimated from
the Newmark method shall correspond to the critical slip surface(s)
established, and with soil properties appropriate for seismic analysis.
Insight into the anticipated Liquefaction Index may be obtained from the
attached Figure 5 that shows the liquefaction susceptibility of soils in
Southwestern British Columbia.
Residual shear strength for liquefied zones should be estimated based on the
charts shown on Figure 6a and 6b. The lower bound strength curves
correspond to sites with relatively thick layers of liquefiable soils that are
overlain by lower-permeability soils that would impede dissipation of excess
pore water pressures.
Figure 6a: Residual Shear Strength Ratio of Soils vs SPT Resistance
(Idriss & Boulanger, 2008).
Page 17
Figure 6b: Residual Shear Strength Ratio of Soils vs CPT Resistance (Idriss &
Boulanger, 2008)
Post-liquefaction vertical settlements should be estimated using the charts
given in Figures 7a and 7b.
Figure 7a: Volumetric Strain of Soils vs SPT Resistance (Mw = 7.5)
Page 18
Figure 7b: Volumetric Strain of Soils vs CPT Resistance (Mw = 7.5)
A pseudo-static seismic coefficient (kh) equal to ½ PGA, residual/liquefied soil
strengths, and minimum FOS of 1.2 shall be considered when the
Liquefaction Index is assessed as L2 or L3 [Ref. Flow Chart shown in
Figure 8].
A pseudo-static seismic coefficient (kh) equal to PGA, reduced soil shear
strengths, and a minimum FOS of 1.0 shall be considered when the
Liquefaction Index is L0 or L1 [Ref. Flow Chart shown in Figure 8].
The proportion of the PGA to be considered, the factor of safety against slope
failure, and the anticipated seismic displacements in the above analyses are
inter-related. Typically, ½ PGA and a factor of safety ranging from 1.1 to 1.3
are considered to result in acceptable seismic displacements [Anderson et al,
2008, NCHRP-611]. These analyses do not explicitly consider effects of
residual excess pore water pressures.
A typical flow chart(s) showing the analysis steps is shown on Figures 8 (a)
through 8 (d). A dike system that is underlain by potentially liquefiable soils
will require several design iterations to satisfy dike integrity and flood
protection requirements.
Page 19
Figure 8a: Data Collection and Evaluation of Liquefaction Index
Page 20
Figure 8b: Typical Analysis Flow Chart for Liquefaction Indices L0/L1
Page 21
Figure 8c: Typical Analysis Flow Chart for Liquefaction Index L2
Page 22
Figure 8d: Typical Analysis Flowchart for Liquefaction Index L3
Page 23
16. Dike
Remediation
Methods
Methods of seismic remediation or strengthening of dikes vary depending
on the modes of failure and/or assessed post-earthquake performance of
the dike-foundation system under consideration. One, or a combination of
several, remediation methods may be utilized to achieve the required
post-seismic performance. These measures are to be implemented
following design and evaluation of dike performance. They may not be
suitable for emergency repair of dikes immediately following a significant
seismic event.
The type of failure mechanism that may be anticipated during and/or
following a seismic event will be dependent on several factors including,
but not limited to, the following:

Nature/distribution of the soil deposits contained within the dike,
beneath and beyond the dike;

Strength, stiffness and sensitivity of the materials within the dike as
well as within the foundation deposits;

Geometric profile of the dike as well as the topographic and
bathymetric surface profiles both upstream and downstream of the
dike; and

Level of water retained by the dike as well as groundwater levels
(phreatic surface) within the dike and the adjacent land.
The designers should consider the factors noted above in the seismic
evaluation of dikes.
The following methods of improving seismic stability of dikes can be
considered in order to meet the performance expectations:

Modify the existing dike profile – Modifying the existing dike profile
may include a combination of raising the dike, widening the dike and
flattening the landside and waterside slopes to reduce the potential for
slope instability during and/or following seismic shaking, or at least
maintain sufficient free board to retain the water contained by the dike
following a major earthquake; and

Implement ground improvement measures – Ground improvement
measures may include densification and strengthening of site soils,
improving drainage to reduce the potential for soil liquefaction and
associated softening, and/or incorporating inclusions into the dike in
the form of sheet piles, secant piles, soil-cement mix panels or jetgrout columns.
The designers should consider one or several methods in combination, for
dike remediation and strengthening, as considered appropriate.
Details of dike remediation and strengthening techniques including the
limitations of each method and equipment are provided in Appendix C.
The data and information used in the dike analysis and findings of the
analyses should be summarized in a report consistent with the Table of
Contents outlined in Appendix E.
Ground improvement methods are costly and may be practical for sections
of dike and appurtenant structures. After the seismic assessment has
been completed, it may be necessary for the Diking Authority to consider
Page 24
the following possible alternatives in situations where the displacement
criteria for dike structure integrity cannot be met:
Re-aligning the dike to avoid the high cost of ground improvement where
the dike is located in seismically vulnerable areas adjacent to steeply
sloping river banks;
Overbuilding the dike provided that the detailed analyses confirm that the
dike core will retain hydraulic integrity (i.e.,. modifying the dike profile as
discussed above); and
Incorporating the dike into massive fills required for adjacent land
development (i.e., the “superdike” concept); again with sufficient analyses
to confirm that the flood protection system would retain its hydraulic
integrity.
17. Threshold
Seismic Event for
Post-Event Dike
Integrity
Inspection
Because seismic design may impact dike alignment and land acquisition
requirements, it is a general recommendation that pre-feasibility
geotechnical studies, including the seismic assessment, be completed
prior to civil design of the dike.
Based on past experience, earthquakes of magnitude Mw ≤ 5.0 are
unlikely to cause liquefaction and significant ground displacements in
earth structures of relatively good workmanship. Figures 9 and 10 show
documented evidence of damage as a function of the earthquake
magnitude versus distance from the source.
Figure 9: Distance from the Fault to Farthest Liquefaction Observed vs
Earthquake Magnitude (Youd, 1991)
Page 25
Figure 10: Distance from Earthquake Epicenter vs Earthquake Magnitude
Causing Damage to Earth Structures (Tani, 1996)
The threshold level of ground surface shaking to cause soil liquefaction
and induce ground displacements of significance is generally estimated to
be about 0.1 g for most locations in Southwestern British Columbia. This
threshold level of shaking can be caused by a number of different pairs of
“Earthquake Magnitude - Epicenter Distance”:
Table 6: Earthquake Magnitude- Epicenter Distance Pairs for Dike
Inspection
Mw 5
occurring within 1 km of the dike
Mw 6
Mw 7
Mw 8.2
Often, the US Geological Survey and Geological Survey of Canada use
the Moment Magnitude (denoted by Mw) to quantify the energy released
by an earthquake. There are other earthquake magnitude scales that
have been and are being used to describe the energy released by an
earthquake; Richter Magnitude (ML), Body Wave Magnitude (mb), Surface
Wave Magnitude (Ms), Japanese Meteorological Agency Magnitude
(MJMA), etc. Most of these magnitude scales correlate well for earthquakes
that vary between magnitude M5 and M7. A typical chart correlating the
different earthquake magnitudes to the Moment Magnitude is shown in
Figure 11.
Page 26
Figure 11: Correlation of Moment Magnitude with other Magnitude Scales
(Youd & Idriss, 1997)
The Modified Mercalli Intensity (MMI) Scale is one of the first scales that
were developed to assess the perceived intensity of earthquake shaking
(as felt by people) and damage.
Peak ground accelerations are
approximately correlated to the MMI scale in the following manner
(Bolt, 1988).
Table 7: Modified Mercalli Intensity Scale Correlated to Damage Potential
and Peak Ground Acceleration
Scale
Shaking Intensity
Damage
PGA
MMI-V
Moderate
Very Light
0.03–0.04 g
MMI-VI
Strong
Light
0.06–0.07 g
MMI-VII
Very Strong
Moderate
0.10–0.15 g
MMI-VIII
Severe
Moderate to Heavy
0.25–0.30 g
MMI-IX
Violent
Heavy
0.50-0.55 g
MMI-X
Extreme
Very Heavy
> 0.60 g
The MMI scale can be used to initiate evaluation of the post-seismic dike
integrity for magnitudes equal to or higher than MMI-VII.
Early information of the occurrence of an earthquake will likely be
available in terms of the earthquake magnitude and epicentral location.
The use of the “Earthquake Magnitude – Epicenter Distance” pairs
described previously are more useful than the MMI scale, to trigger dike
integrity inspections. A typical event notification from the US Geological
Page 27
Survey is reproduced below for information:
== PRELIMINARY EARTHQUAKE REPORT ==
***This event supersedes event AT00992705.
Region: VANCOUVER ISLAND, CANADA REGION
Geographic coordinates: 50.218N, 129.535W
Magnitude: 6.1 Mw
Depth: 10 km
Universal Time (UTC): 28 Aug 2008 12:37:35
Time near the Epicenter: 28 Aug 2008 05:37:35
Local standard time in your area: 28 Aug 2008 12:37:35
Location with respect to nearby cities:
153 km (95 miles) WSW (251 degrees) of Port Hardy, BC, Canada
308 km (191 miles) W (276 degrees) of Campbell River, British Columbia,
Canada
412 km (256 miles) WNW (302 degrees) of Neah Bay, WA
472 km (293 miles) WNW (285 degrees) of Vancouver, British Columbia,
Canada
Post-seismic dike integrity evaluation work should be triggered for any of
the earthquake magnitude – epicenter distance pairs identified in Table 6.
Details on dike inspection and subsequent engineering evaluations are
presented in Appendix B.
18. PostEarthquake
Emergency
Repair of Dikes
The post-earthquake breach of a dike can occur due to overtopping,
piping and seepage, and sliding and foundation failure.
Infilling by placing and compacting of suitable fills into the zone of
disturbance/failure caused by the breach, placing sand bags, and the use
of water-filled fabric tubes are considered to be practical remedial
measures for emergency dike repair. Details are provided in Appendix D.
There is a low probability of a seismic event with a long return period
(i.e.,. a rare event) and large peak ground accelerations occurring
concurrently with the high water levels in the Fraser River during the
spring snowmelt freshet.
The post-earthquake emergency repair
measures are intended to provide flood relief over the period in between
the seismic event and freshet time when the available time to implement
permanent dike rehabilitation and strength is inadequate.
19. References
1. Youd, T. L., Idriss I. M., Andrus, R. D., Arango, I., Castro, G.,
Christian, J. T., Dobry, R., Finn, W. D. L., Harder, L. F., Hynes, M. F.,
Ishihara, K., Koester J. P., Liao, S. S., Marcuson, W. F., Martin, G. R.,
Mitchell, J. K., Moriwaki, Y., Power, M. S., Robertson, P. K., Seed, R.
B., and Stokoe, K. H., 2001. Liquefaction Resistance of Soils:
Summary Report from the 1996 NCEER and 1998 NCEER/NSF
Workshops on Evaluation of Liquefaction Resistance of Soils, Journal
of Geotechnical and Geo-environmental Engineering, ASCE 127(10),
pp. 817-833.
Page 28
2. Idriss, I.M. and Boulanger, R.W. 2008. Soil liquefaction during
earthquakes, EERI Mongraph MNO-12.
3. Anderson D. G., Martin G. R., Lam, I., and Wang, J. 2008, Seismic
Analysis and Design nof Retaining Walls, B uried Structures, Slopes,
and Embankments, NCHRP Report 611, Transportation Research
Board, Washington D C, USA.
4. Youd, T.L. and Idriss, I.M. eds. 1997. Proceedings of the NCEER
Workshop on Evaluation of Liquefaction Resistance of Soils, Technical
Report NCEER-97-0022, Multidisciplinary Center for Earthquake
Engineering Research, Buffalo, New York, 276 p.
5. Faccioli, E. 1991. Seismic amplification in the presence of geological
and topographic irregularities, Proceedings of the Second International
Conference on Recent Advances in Geotechnical Earthquake
Engineering and Soil Dynamics, University of Missourri-Rolla, St.
Louis, Missouri, pp. 1779-1797.
6. Tani, S., 1996. Damage to earth dams, Special Issue of Soils and
Foundations, Japanese Geotechnical Society, pp. 263-272.
7. Youd, T.L., 1991, Mapping of Earthquake-Induced Liquefaction for
Microzonation, Fourth International Conference on Microzonation,
Stanford, California.
8. Youd, T.L. and Perkins, D.M., 1987, Mapping of Liquefaction Severity
Index Journal of Geotechnical Engineering, Vol. 113, No11, pp 13741392.
9. Newmark, N.M., 1965, Effects of Earthquakes on dams and
embankments, Geotechnique, Vol 29, No 3, p 215-263.
10. Seed, H. B., and Idriss, I. M., 1971, "Simplified procedure for
evaluating soil liquefaction potential." J. Soil Mechanics and
Foundations Div., ASCE 97(SM9), 1249–273.
11. Idriss, I.M. and Boulanger, W. 2004, ”Semi-Empirical Procedures for
Evaluating Liquefaction Potential During Earthquakes.” Proceedings
of the 11th international Conference on Soil Dynamics and Earthquake
Engineering and the 3rd International Conference on Earthquake
Geotechnical Engineering, Univ. of California, Berkley, CA, 2004.
12. Bolt, Bruce A (1988), “Earthquakes”, W. H. Freeman and Company.
13. Wood H. O. and Neumann F. (1931), “Modified Mercalli Intensity Scale
of 1931”, Seismological Society of America Bulletin, Vol. 53, No. 5, pp.
979-987.
Figure 1: Dike Locations in the Fraser ValleyFigure 5: Liquefaction Susceptibility
O:\Final\2010\1447\10-1447-0333 (Seismic)\1014470333-003-R-Rev2\1014470333-003-R-Rev2 Seismic Guidelines Dikes 11JUN_14.docx
Page 29
520000
540000
560000
480000
500000
520000
540000
560000
580000
5440000
LEGEND
RIP RAP
STANDARD DIKE
NON-STANDARD DIKE
5420000
5420000
N:\Bur-Graphics\Projects\2010\1447\10-1447-0333\GIS\projects\figure-01_dike-locations.mxd
5440000
5460000
500000
5460000
480000
580000
6
MAJOR ROAD
MUNICIPAL BOUNDARY
0
SCALE 1:300,000
PROJECT
OTHER FLOOD CONTROL WORKS
FISH AND WILDLIFE WATER RELATED STRUCTURE
6
KILOMETRES
TITLE
REFERENCE
LOWER MAINLAND DIKE INVENTORY DATA OBTAINED FROM THE MINISTRY OF ENVIRONMENT (MOE), WATER STEWARDSHIP DIVISION,
FLOOD HAZARD MANAGEMENT, COASTAL REGION. ROAD AND MUNICIPAL BOUNDARY DATA OBTAINED FROM DMTI SPATIAL INC.
SHADED RELIEF OBTAINED FROM ESRI.
DATUM: NAD83 PROJECTION: UTM ZONE 10
MINISTRY OF FORESTS,
LANDS AND NATURAL
RESOURCE OPERATIONS
FLOOD SAFETY SECTION
DIKE LOCATIONS IN THE FRASER VALLEY
PROJECT
DESIGN
Greater Vancouver Office, B.C.
BM
GIS
CDB
REVIEW
UA
CHECK
BM
10-1447-0333
13JUN11
13JUN11
09AUG11
09AUG11
FILE No.
SCALE AS SHOWN
REV.
FIGURE 1
0
500000
520000
540000
560000
500000
520000
540000
560000
580000
5460000
5460000
480000
See Note A
5440000
LEGEND
480000
PUMP STATION
TREATMENT PLANT
RIP RAP
STANDARD DIKE
NON-STANDARD DIKE
OTHER FLOOD CONTROL WORKS
FISH AND WILDLIFE WATER RELATED STRUCTURE
PIPELINE
REFERENCE
580000
6
MAJOR ROAD
MUNICIPAL BOUNDARY
PROJECT
LOW TO VERY HIGH
VERY HIGH
HIGH
6
KILOMETRES
TITLE
MODERATE
LOW
LOWER MAINLAND DIKE INVENTORY DATA OBTAINED FROM THE MINISTRY OF ENVIRONMENT (MOE), WATER STEWARDSHIP DIVISION,
FLOOD HAZARD MANAGEMENT, COASTAL REGION. SURFICIAL GEOLOGY DATA OBTAINED FROM THE GEOLOGICAL SURVEY OF CANADA.
ROAD AND MUNICIPAL BOUNDARY DATA OBTAINED FROM DMTI SPATIAL INC. PUMP STATION, TREATMENT PLANT, AND PIPELINE DATA
OBTAINED FROM GREATER VANCOUVER SEWERAGE AND DRAINAGE DISTRICT. SHADED RELIEF OBTAINED FROM ESRI.
DATUM: NAD83 PROJECTION: UTM ZONE 10
0
SCALE 1:300,000
RELATIVE LIQUEFACTION SUSCEPTIBILITY RATING
VERY LOW
5420000
5420000
N:\Bur-Graphics\Projects\2010\1447\10-1447-0333\GIS\projects\figure-05_liquefaction-susceptibility.mxd
5440000
See Note A
NOTE
A. INFERRED SOIL CONDITIONS BASED
ON GSC SURFICIAL GEOLOGY MAP.
MINISTRY OF FORESTS,
LANDS AND NATURAL
RESOURCE OPERATIONS
FLOOD SAFETY SECTION
LIQUEFACTION SUSCEPTIBILITY
PROJECT
DESIGN
Greater Vancouver Office, B.C.
BM
GIS
CDB
REVIEW
UA
CHECK
BM
10-1447-0333
13JUN11
13JUN11
09AUG11
09AUG11
FILE No.
SCALE AS SHOWN
REV.
FIGURE 5
0
APPENDIX A
Literature Review of Seismic Design Guidelines
for Flood Protection Dikes
APPENDIX A
Literature Review of Seismic Design Guidelines for Flood Protection Dikes
A1.0 INTRODUCTION
Using dikes as a form of flood protection is common in many areas of the world. However, the art of dike design
and construction has been developed and initiated predominantly in three countries, namely the USA, Japan,
and the Netherlands. In particular, the design issues relating to earthquake performance of dikes is limited to
mainly the west coast and the central Mississippi area of the USA and Japan. A review of information relating to
flood protection dikes indicates that a plethora of information exists in the USA and to some extent in both the
Netherlands and Japan.
A2.0 EVOLUTION OF DESIGN PHILOSOPHY FOR FLOOD PROTECTION
DIKES
Many dikes were originally constructed without major engineering design input and really developed as grass
roots construction projects to prevent flooding. In the USA, the age of the dikes throughout the country can vary
from recent upgrading of about 50 years ago to in excess of 100 years where very little additional work has been
done over that period. In the USA, where lesser standards have been historically applied, it is evident that better
safety standards are required and more formalized approaches are necessary. The Netherlands, USA and
Japan have recently started to formalize their approach to design and upgrading of dikes.
Historically, dikes have been designed using traditional design methods such as slope stability analysis and
factor of safety criteria considering higher than average loading applied to the dike and lower resistances (soil
strengths) within the dike structure and underlying foundation soils. These factors of safety have inherently built
in acceptable values of societal risk although not specifically defined. More recently, however, societal risk is
being assessed by following the approaches described below:

Using a performance-based approach by adopting a classification system for the dikes based on
importance; establishing multiple levels of ground shaking varying from frequently occurring to rarely
occurring ground motions; and thereafter establishing performance expectations for each level of ground
shaking and for each importance category of dikes (see Figure A-1, Note: 1000 gal = 1 g); and

Using risk assessment and risk management by specifying probability of particular types of failure or,
alternatively, the reliability of particular components with respect to various functions.
Figure A-1: Evolution of Design Concepts and Methods of Analysis (Ishihara, 2009).
June 2014
Reference No. 1014470333-003-R-Rev2
1/8
APPENDIX A
A2.1 Performance-Based Design Philosophy
In Japan, the Ministry of Land Infrastructure and Transport developed a policy for “Performance–Based Seismic
Design Criteria for River Facilities” (ref. Sugita and Tamura, 2007). This policy has formulated an approach
where the dike system is classified into simple categories on whether the structure is important for flood control
and whether or not alternative measures are available if the dike was no longer functioning. The required
performance level of the dike is then defined and the relevant return period for design established based on the
importance of the structure. Calculations must then be carried out for stability and settlement to assure that the
dike will continue to function during and/or following the design level earthquake accelerations as per the
consequence classification. They identify two different levels of ground shaking (earthquake accelerations) and
three levels of performance expectations:
Earthquake Levels
Level 1 Earthquake:
Ground motions that occur with a high probability during the service life of the structure;
and
Level 2 Earthquake:
Maximum credible ground motions at the site
Performance Levels
Performance Level 1:
The structure or component does not lose soundness as a river facility;
The structure retains function as a river facility against the water level defined for
assessing seismic performance; and
The structure experiences limited damage and repair to damages can be made within a
short time.
Typical criteria for seismic displacements and remaining free-board along with the post-event flood protection
capability of the dike (or performance), proposed by the US Army Corps of Engineers for urban and urbanizing
areas, are summarized below (Koester, 2010A):
Amount of
Deformation
Significant Damage to
Internal Structures
Remaining Freeboard for
Post-Seismic Evaluation
Post-Seismic Protection
Ability
< 0.3 m
No
>0.3 m
Probably Uncompromised
0.3 to 0.9 m
Possibly
>0.3 m
Possibly Uncompromised
0.9 to 3 m
Likely if existing
None
Likely Compromised
Unlimited
Yes
None
Compromised
June 2014
2/8
APPENDIX A
A2.2 Risk-Based Design Philosophy
Modern engineering practice such as probabilistic, modeling, and failure mode analysis along with risk
considerations, described in the latter approach, are now the normal approach to dam design and construction.
These techniques indicate that better safety standards and practices are generally needed. The risk of flooding
in different areas has resulted in different standards being adopted depending on the risk that the community is
prepared to accept. For example, loss of dike protection in the Netherlands can be catastrophic for the country,
the amount of risk that the country is prepared to assume has to be low and dictates that the design flood levels
accepted for dike design are much higher than in other areas.
Under current practice in the USA, the approach to dike design considers a combined probabilistic and
deterministic approach that utilizes conditional risk and uncertainty based on water levels for carrying out
deterministic dike analyses. There are efforts currently underway to develop new risk-based approaches to dike
design. The approach to design is contained in the US Corps Engineering Design Manual EM 1110-2-1913
“Design and Construction of Levees” (US Army Corps of Engineers, 2000). This approach is currently under
development and not as yet formalized. This design manual does not specifically require consideration of
earthquakes “because of the low probability of earthquake coinciding with periods of high water” but makes a
statement that “depending on the severity of the earthquake and the importance of the levee, seismic analysis to
determine liquefaction susceptibility may be required. In high earthquake zones this analysis might therefore be
required”.
Recommendations from the National Committee on Levee Safety has indicated that a classification system for
dike design be adopted and further states that the current classification system is interim with the intent that
there will be a future need to classify dikes by potential hazard and risk in order to set appropriate design criteria
and requirements. An example of a hazard potential classification proposed by the National Committee on
Levee Safety is as follows:
Table A-1: Example Hazard Potential Classification (Ref. Report to US Congress on Recommendations
for National Levee Safety program, 2009)
Hazard Potential
Classification
High
Number of
People
Potentially
Inundated to
Depths > 3 feet
Number of
People
Potentially
Inundated
> 10,000
Additional Considerations
> 10,000
Includes areas of consequence where critical life
safety infrastructure is at risk (e.g. major
hospitals, regional water treatment plants, and
major power plants)
Significant
> 1,000
< 10,000
Includes areas of consequence where the
number of people potentially included is low, but
there may be significant potential for large
economic impacts or losses
Low
< 1,000
0
-
June 2014
3/8
APPENDIX A
A3.0 RISK-BASED APPROACH
A risk-based approach is considered a better method to both assess the requirements of flood control dikes and
prioritize available upgrading and maintenance funds. This approach will allow funds to be allocated in a manner
consistent with the potential risk of damage and loss of life. Future risks to dikes come from the following major
components:



The likelihood of floods;
The likelihood that the dikes will not perform as designed or intended; and
The consequence as a result of failure on people property and environment.
Tolerable societal risk is inherent in all we do as individuals. We do not in general attempt to quantify these risks
and passively accept them in going about our daily lives. However, mathematically they can be quantified as is
done for insurance actuary purposes. The process that puts all components of risk as discussed above into a
societal context enables better decision making in comparison with other published risk guidelines; e.g. the
airline industry, dam safety programs, transportation, and medicine.
In seismic considerations, the general risk assessment procedure consists of the following:



Probability of ground motions at the dike site;
Probability of dike rupture due to failure; and
The expected loss (in $$) due to failure.
The probability of dike failure is a function of dike slope deformations as shown below on Figure A-2
(Rosidi, 2007)
Figure A-2: Example of a Levee Fragility Curve (Rosidi 2007).
June 2014
4/8
APPENDIX A
The conditions that define failure include, piping (internal erosion) overtopping, cracking, slope, slope sliding and
settlement. The suspected damage to a dike under earthquake motions is estimated by integrating the
probabilities of failure considering all the various conditions that contribute to a failure such as site conditions,
dike construction materials, water levels, and earthquake ground motions. A logic tree approach is frequently
used as shown on Figure A-3.
SEISMIC VULNERABILITY EVALUATION
Section
PGA
Operating
Scenario
Liquefaction
Controls
Response
Field
Acceleration
Max Ave.
Acceleration
Ky(liq)
Kmax
Ave.
Acceleration
Time History
Displacement
Failure
Probability
Disp-1
FP-1
Disp-2
FP-2
Low tide
high reservoir
weight = 0.34
0.14 g
Section nth
Yes
43 -yr RP
0.33 g
High tide
low reservoir
Kave.-1
475 –yr RP
weight = 0.66
weight = 0.5
0.52 g
No
Ky(non-liq)
Kmax
2,500 –yr RP
Kave-2
Mean Failure Probability for segment nth
=�
𝑖
weight = 0.5
�(𝑃𝐺𝐴)𝑖 (𝑂𝑝𝑒𝑟)𝑗 ��𝑃𝑙𝑖𝑞 �[𝐹𝑝(𝑑𝑖𝑠𝑖𝑗𝑘 )] + �1 − 𝑃𝑙𝑖𝑞 �[𝐹𝑝�𝑑𝑖𝑠𝑖𝑗𝑘 �]
𝑗
𝑘
Figure A-3: Logic Tree Approach for Integrating the Results of Various Assumptions (Rosidi, 2007).
The intent of tolerable risk assessments adopts the concepts of Equity and Efficiency as shown on Figure A-4.
Figure A-4: Concept of Equity and Efficiency (NCLS, 2009).
June 2014
5/8
APPENDIX A
A4.0 FLOOD LEVEL AND FREEBOARD
Design criteria for flood levels are variable throughout the world. In particular the design flood levels in the USA
(currently FEMA considers a 1:200-year design flood level as a minimum, Halpin et al. 2009) are much lower
than in the Netherlands where a minimum 1:1,250-year design flood level for river dikes has been adopted
(Ten Brinke, W.B.M, et al, 2010). The dike performance is assessed using the traditional design criteria in terms
of factors of safety.
Draft guidelines prepared by the California Department of Water Resources (August, 2008) for Urban and
Urbanizing Area State-Federal Project Levees (FEMA, 2008), consider levees in the deltas differently, where
there is a high likelihood of having coincidental high water and earthquake loading. Levees which infrequently
experience loading from high water are proposed to be evaluated using typical water surface elevations.
In addition to the flood level, freeboard requirements also vary throughout the various countries. Recent concern
about sea level rise from global warning has resulted in significant upgrading of the freeboard of the Dutch dikes.
In the USA, FEMA has adopted the National Flood Insurance Program (NFIP) regulations that require no dike
freeboard to be less than 0.6 m (2 feet) and in general 1 m (3 feet).
The Japanese performance-based design criteria consider the “highest daily water level under usual conditions”
in the seismic performance of river facilities. This water level is established considering that the earthquake and
flood would not occur simultaneously. Around river mouth or delta areas, the water level considered would
include the combination of the highest tidal water level, the wind waves and a tsunami wave.
A5.0 SEISMIC SHAKING
Seismic performance of dikes has generally been ignored in most countries in the past, except in specific cases.
The USA procedures have in general neglected to consider seismicity except in California and in the Mississippi
Delta (FEMA, 2008). In Japan there is a much greater appreciation for seismic design of dikes and
consequently there has been more focus on seismic considerations in dike design (Koester 2010B). In the
Netherlands, the country is considered to be very benign with respect to earthquakes and because of low
probability, seismic effects on dikes are not considered in their design criteria.
In the USA, current thinking for dikes that infrequently experience loading from high water is to accommodate the
earthquake risk by providing efficient and prompt post-earthquake dike repair and flood response. Ground
remediation for liquefaction prevention might be considered in some extreme cases (FEMA, 2008). For repair
and improvement work associated with urban and urbanizing area levees, seismic ground motions having a
return period of 200-years are being proposed. Furthermore, repairs for improvements primarily for the purpose
of seismic strengthening are generally not considered to be justifiable for levees that are subjected to only
seasonal high water loading.
Draft engineering and design guidelines developed by the US Army Corps of Engineers for certification of levee
systems for the national flood insurance program (NFIP) consider that levee systems located in regions which
experience strong ground motions from earthquake activity should consider seismic effects on the stability of
dikes. They have adopted ground motions with a return period of 475-years for seismic design with the provision
that if the PGA is not greater than 0.15 g, no evaluation is required. For PGAs greater than 0.15 g, the levee and
its foundation are to be checked for liquefaction using a simplified procedure such as the Simplified Seed
Method (Seed and Idriss, 1971).
June 2014
6/8
APPENDIX A
In Japan, the requirements are that dikes shall be assessed considering the appropriate earthquake design
motions consistent with the performance level deemed appropriate for the dike under consideration. River
facilities such as levees should consider seismic ground motions that have a “high probability of occurrence
during the service life” as well as “maximum credible ground motions” with expected performance descriptors
attached to each level of shaking.
June 2014
7/8
APPENDIX A
REFERENCES:

Ishihara, K. 2009. Perspectives in Geotechnics for Vastly Strong Earthquake Shaking, Special Discussion
Session, Future Performance-Based Design, Taylor and Francis Group, London, UK.

Sugita, H. and Tamura, K. 2007. Development of seismic design criteria for river facilities against large
earthquakes. Earthquake Disaster Prevention Research Group, Japan.

Koester, J.P. 2010A. Seismic activity and vulnerabilities to levees, 2010 Missouri River/Texoma Regional
and Midwest Levee Conference.

US Army Corps of Engineers. 2000. US Army Corps Engineering Manual EM 1110-2-1913, Design and
construction of levees.

Rosidi,D. 2007 Seismic Risk Assessment for Levees, Civil Engineering Dimension, Vol 9, No2 , pp 57-63

National Committee on Levee Safety (NCLS). 2009. Recommendations for a National Levee Safety
Program (Draft Report to US Congress).

Ten Brinke, W.B.M, Kolen, B., Dollee, A., Van Waveren, H. and Wouters, H. 2010. Contingency planning
for large-scale floods in the Netherlands. Journal of Contingencies and Crisis Management, Vol. 18, Issue
2, pp. 55-69.

Halpin, E., Becker, B., Harkness, A., and Snorteland, N. 2009. Joint development of a risk management
rd
and assessment strategy for federal dam and levee owners. 23 ICOLD Conference, Brazil, Q91-R55.

FEMA 2008. Proposed interim design criteria for urban and urbanizing state-federal project levees.

Koester, J.P. 2010B. USACE Earthquake research and implementation activities, US Army Corps of
Engineers.

Seed, H.B. and Idriss, I.M. 1971. Simplified procedure for the evaluation of soil liquefaction potential.
Journal of Soil Mechanics and Foundation Division, ASCE, Vol. 107, SM9, pp. 1249-1274.
o:\final\2010\1447\10-1447-0333 (seismic)\1014470333-003-r-rev2\component\appendix a - final draft.docx
June 2014
8/8
APPENDIX B
Earthquake Inspection Checklist
APPENDIX B
B1.0 INTRODUCTION
An earthquake may cause failure or severe damage to a dike and its appurtenant structures. In the event of
damage, immediate action may be necessary to prevent further weakening or catastrophic failure of the
structure. Accordingly, all diking districts personnel should be carefully instructed in the procedures to be
followed if an earthquake should occur that produces motions of intensity sufficient to possibly cause damage.
There are two phases of the inspection procedure:
1)
An immediate inspection; and
2)
Follow-up inspections.
The general procedures described herein may be used as guidelines.
B2.0 INSPECTION IMMEDIATELY FOLLOWING AN EARTHQUAKE
If an earthquake is felt on/or near the dike, or has been reported to have occurred, with a moment magnitude of,
Mw 5 or greater within 1 km, Mw 6 or greater within 8 km, Mw 7 or greater within a 50 km, Mw 8+ or greater within
180 km radius from the site, follow these procedures:

Immediately make an overall inspection of the dikes. Check the dike for sloughs, slides, cracks,
displacements, settlements, sinkholes, springs or seeps, and other signs of distress.

If the dike appears to be damaged to the extent that there is increased or new flow passing downstream,
report immediately.
If visible damage has occurred but, in the best judgment of the inspector, is clearly not serious enough to cause
failure of the dike, the nature, location, and extent of damage should be observed and the rate of any change
recorded.
Thoroughly inspect the damage using the following checklist:

Check the crest and both faces of the dike for cracks, settlement, displacement or seepage;

Check the land side of the dike for visible landslides, new springs and sand boils;

Check drains and seeps for increased flow or stoppage of flow; and

Check structures and pumping equipment for misalignment and distress.
June 2014
1/4
APPENDIX B
If no apparent damage has occurred to the dike embankment, or appurtenant structures, make a “No Damage”
report. Continue to inspect and monitor the facilities for at least 48 hours. Some damage to structures may not
be readily apparent during an inspection immediately following an earthquake. It is possible that settlement of
structures, reactivation of old slides, or development of new slides or springs/seeps may not have occurred
during ground shaking, but could appear after the initial inspection. A secondary inspection should be carried
out two (2) weeks to a month after the initial inspection.
B3.0 ENGINEERING FOLLOW-UP INSPECTION
In the event that an inspector reports that damage has occurred or a dike has been severely shaken, qualified
engineering and geologic personnel should be dispatched as rapidly as possible to the site to make a technical
evaluation of the extent of damage and the degree of hazard it presents. The members of such an inspection
team should be familiar with the possible modes and causes of failures, and should also be familiar with the
main features of the project.
B3.1 Possible Modes and Causes of Dike Failures
The members of an inspection team must be aware of the modes of dike failures, both static and dynamic.
Team members should have had some training in dike failures, both static and dynamic to reinforce their
engineering understanding of why failures occur.
Some of the more common causes of static and dynamic failures of dikes and examples of adverse conditions
are discussed in this section. Adverse conditions that can lead to failure are categorized as follows:
Failure Category
Foundation Instability
Causes
Liquefaction
Slides
Removal of solid and/or soluble materials by water subsidence
differential settlement
Joint openings and/or grout curtain rupturing movement on faults
under or adjacent to dikes
Defective Flood Control Structures
Obstructions
Damaged structure walls, slabs
Crushed or deteriorated concrete
Embankment Dike Defects
Liquefaction
Slope instability
Excessive seepage
Removal of solid and/or soluble material surface soil erosion caused
by overtopping embankment settlement producing inadequate
freeboard for required spillway capacity cracks or sinkholes
June 2014
2/4
APPENDIX B
B3.2 Foundation Deficiencies
These deficiencies are associated with the geotechnical condition of the foundation materials or with the
foundation design of the dikes. Differential settlement, slides, excessive pressures, weak layers or zones, and
inadequate control of seepage are all potential failure mechanisms within a foundation. Foundation conditions,
which have low shear strength or seams of weak material such as shales, bentonitic materials, or faults, can
result in sliding of the foundation and embankment. Also, thin highly permeable layers in the foundation, which
have no provisions for pressure relief allow transmission of excessive uplift pressures and cause sliding.
Seepage through the dike foundation can cause piping or internal erosion of soil. Such removal of foundation
material forms voids, which can increase until a portion of the remaining unsupported material collapses and
failure of a section of the foundation occurs. Water can also cause a breakdown of some foundation materials
such as shales, or reduce the shear strength of bedrock.
Some of these weaknesses can be identified by visual examination of the foundation conditions. Visible cracks
in a dike embankment can be indicative of foundation movement. Visual evidence of piping is sediment in the
seepage water.
B3.3 Flood Control Outlet Works
Many adverse conditions such as obstructions to the flow, structural weaknesses, or faulty drains can be
identified by visual examination. Structural failure in a conduit or, other structure could obstruct the flow in the
system. Loss of the power source to operate facilities such as pumps may also present operational conditions,
which compromise the safety of the dike.
Slides from the slopes above flood boxes etc. can block approach channels and also damage intake structures
and associated mechanical equipment.
Cracking and movement of concrete structures may indicate distress.
B3.4 Seepage
Uncontrolled seepage through the dike embankment or foundation can result in excess pore pressures which
weaken the soil mass and may cause springs, boils, or slope failures and/or the movement of soil particles to
unfiltered exits, creating voids which can lead to a piping failure. The “pipes” or “tunnels” under a dike also can
cause the collapse of surrounding materials. This can then lead to the formation of settlement cracks or,
ultimately, to breaching of the embankment.
B3.5 Detective or Inferior Materials
Low-density, saturated, cohensionless soils in an embankment or foundation can experience liquefaction due to
an increase in pore pressure and loss in shear strength when subjected to earthquake-induced shear stresses.
Depending on a variety of factors, including material properties and in-place conditions, pre-earthquake stress
conditions, and magnitude and duration or seismically-induced stresses, the dike or its foundation can exhibit
instability, settlement, and subsequent loss of freeboard.
June 2014
3/4
APPENDIX B
B3.6 Appurtenant Structures
All appurtenant structures that could affect the safe operation of the dike should be examined.
Approach channels are usually submerged and may require special underwater investigation. Channel erosion
protection such as rip rap should be checked to determine if the protection is still functional.
All channels should be examined for evidence of sinkholes, boils or piping and should provide satisfactory
clearance around flood control and pumping structures so the structures can operate as designed.
Fill adjacent to flood control structures should be examined for subsidence caused by soil movement, and
contacts between the fill and the structures should be examined for evidence of piping or voids. Cut or fill slopes
adjacent to the structures should be examined for unstable conditions such as sloughs, slides, debris and the
like.
B4.0 REFERENCES
US Committee On Large Dams (USCOLD). 1984. Bibliography on Performance of Dams during Earthquakes.
US Committee On Large Dams (USCOLD). 1992. Observed Performance of Dams during Earthquakes.
US Committee On Large Dams (USCOLD). 1995. Guidelines for Earthquake Design and Evaluation of
Structures Appurtenant to Dams.
US Committee On Large Dams (USCOLD), Observed Performance of Dams during Earthquakes, Volume II.
(2000).
US Society on Dams (USSD). 2003. Guidelines on Design Features of Dams to Effectively Resist Seismic
Ground Motions.
o:\final\2010\1447\10-1447-0333 (seismic)\1014470333-003-r-rev2\component\appendix b - final draft.docx
June 2014
4/4
APPENDIX C
Failure Mechanics and Ground Treatment
Methods
APPENDIX C
Failure Mechanics and Ground Treatment Methods
C1.0 INTRODUCTION
In addition to the traditional static and hydraulic modes of failure routinely reviewed for new dike construction
and/or dike upgrades, a review of the potential modes of dike failure that may be generated by earthquake
induced ground motions should be considered as part of the seismic evaluation of the dike stability. The type of
failure mechanism that may be anticipated during and/or following a seismic event will be dependent on several
factors including, but not limited to:

The nature/distribution of the soil deposits contained within the dike, beneath and beyond the dike;

The strength, stiffness and sensitivity of the materials within the dike as well as within the foundation
deposits;

The geometric profile of the dike as well as the topographic and bathymetric surface profiles both upstream
and downstream of the dike; and

The level of water retained by the dike as well as groundwater levels (phreatic surface) within the dike and
the adjacent land.
The above information coupled with the required performance criteria stipulated for specified or select seismic
hazards would be relied upon for assessing potential failure mechanisms that may develop in response to
seismic induced motions along the dike. Some examples of failure mechanisms that may be caused by
earthquake induced ground motions are:

A disruption or stepwise shearing of the dike caused by slip or thrust fault movement within the foundation
materials;

Significant loss of strength of soils within, beneath and/or beyond the dike structure as a result of
liquefaction, cyclic softening and/or cyclic mobility;

Bearing capacity failure of the dike due to significant weakening of the foundation deposits;

Slope failures induced by ground motions and/or weakening of the underlying deposits;

Translational sliding of the dike on weak foundation soils;

Piping failures through cracks induced by ground movements;

Overtopping of dikes due to seiches and/or tsunamis;

Overtopping of dikes due to water course obstructions such as a slide; and

Loss of free board due to settlement or differential ground movements resulting from bearing or slope
failure, or other ground induced differential movements.
A brief discussion of various earthquake induced failure mechanisms that may affect the integrity of dike systems
are presented below.
June 2014
1/15
APPENDIX C
C1.1 Fault Movement
The energy released from movement along a fault is the cause of most earthquakes. There are several different
types of faults within the earth’s crust that include:
1)
Dip-slip fault – where relative movement along the discontinuity is approximately vertical;
2)
Strike-slip fault – where relative movement along the discontinuity is generally horizontal; and
3)
Oblique – slip fault has components of both the strike and dip slip fault.
The potential damage to a dike system generated by any of the three types of fault movements described above
would likely manifest as a “stepwise” or shear displacement of the structure which can be in the order of several
metres long.
C1.2 Liquefaction/Cyclic Softening/Cyclic Mobility
C1.2.1
Liquefaction
Liquefaction represents a phase change within a material from a solid or gas to a liquid resulting from change in
external pressures. In soil deposits, liquefaction occurs within saturated, predominantly granular soil materials
when water contained within the soil pores is pressurized to a level consistent with the total overburden stress
within the soil deposits. Such conditions can prevail under static conditions when hydraulic gradients within the
deposits are high. An example of static liquefaction is “quick sand” or “sand boils” that are frequently associated
with excessive hydraulic gradients at, or near the downstream toe of the dikes. Under dynamic conditions,
excess pore water pressures are created by a volumetric change occurring within the soil structure resulting from
contractive behaviour of the deposits during cyclic shaking. Depending on the extent of liquefaction and
geometric profiles of the surface conditions, liquefaction can lead to local (bearing) failure and/or global (flow)
failure of the deposits, particularly where imposed static shear stresses are greater than the post liquefied
(undrained residual) strength of the deposits.
Similar to contractive granular deposits, highly sensitive deposits containing a mixture of clays and silts may also
experience “liquefaction type” failures. Typical characteristics of highly sensitive fine-grained deposits include a
high to very high moisture content and a significant strength variation between small strain (peak) strength and
large strain (remoulded) strength. Examples of sensitive fine-grained deposits are “quick” clays, such as the
Leda Clays and Champlain Clays found in Eastern Canada and the Still Creek Clay deposits in Burnaby, BC.
Similar to liquefaction, a sudden, abrupt loss of strength resulting from cyclic shaking can lead to bearing and/or
flow type failures.
June 2014
2/15
APPENDIX C
C1.2.2
Cyclic Softening
Cyclic softening is generally associated with temporary (transient) strength loss of deposits during cyclic shaking.
Deposits which generally exhibit this type of strength reduction are fine-grain, predominantly silt deposits. Unlike
highly sensitive clays and contractive (loose) granular deposits, cyclic straining of silts generally do not result in
flow slides associated with liquefaction, but may experience large deformations during pore pressure build-up.
The main difference between liquefaction and cyclic softening is that deformations do not continue after cyclic
loading ceases. Deformations predominantly occur when the combined static and inertial (earthquake induced)
stresses exceed the transient strength loss of the silt deposits. As deformation occurs, dilative (opposite of
contractive) conditions develop resulting in a reduction in pore pressure allowing for strength gain to at, or near
pre-earthquake conditions. Consequently, deformations generally manifest as a progressive “ratcheting” type of
movement.
C1.2.3
Cyclic Mobility
Cyclic mobility is generally associated with loose to dense unsaturated granular deposits, firm to hard,
insensitive fine-grained (silty clay, clayey silt) deposits and/or dense, saturated deposits. Cyclic mobility occurs
when continued cyclic shear strain results in a dilative response caused by limited pore pressure build-up in
unsaturated soil conditions and/or following a brief contraction of the soil particles, such as the case with dense
to very dense saturated sands. Deformations accumulate in each cycle of shear stress; however, the magnitude
of the accumulated deformations are typically quite small relative to displacements generated by liquefaction
and/or cyclic softening.
C1.3 Bearing Capacity Failure
Bearing capacity failure is a sudden or an abrupt loss of local support of the foundation soils as a result of static
shear stress within the foundation materials exceeding the shear strength of the deposits. Under seismic
conditions, bearing capacity failure may occur when liquefaction develops within the foundation materials
resulting in a substantial loss of shear strength. Bearing capacity failure may be manifested as a local rotational
slip of the foundation or a “punching” or plunging type failure. Both failure mechanisms can result in a significant
reduction in the dike crest elevation. The predominant displacements generally occur within the vertical axis
compared to the horizontal axis. Illustrative examples of bearing capacity are presented below.
Figure C1-a: Local Bearing Failure
June 2014
Figure C1b: Punching Shear Failure
3/15
APPENDIX C
C1.4 Slope Stability Failure
Similar to bearing capacity failure, slope instability occurs when the static and/or combined static and dynamic
shear stresses within a sloping soil mass exceeds the net shear resistance of the deposits along a select slip
plane. Unlike bearing capacity failure, a slope failure movement generally occurs in a discreet direction
potentially resulting in significant vertical and horizontal displacements, with the horizontal displacement vector
generally representing the predominant movement axis. Slope stability also generally relates to massive or
global failure mechanism compared with local conditions with bearing capacity. Consequently, the condition of
the deposits at significant depth can affect slope stability. The most common slip surfaces associated with slope
stability are circular or arc shaped; however, depending on the distribution of soil types and strengths below the
slope surfaces, failure slip surfaces can be also be planar or multi-planar. The following figure presents a typical
circular slip failure.
Figure C-2: Global Stability Failure, Circular Slip- Surface.
C1.5 Translational Sliding
Translational sliding is a form of slope instability that represents predominantly horizontal (planar) movement
with limited vertical displacement. Such conditions can develop within horizontally stratified deposits of variable
strengths and thicknesses or zones of liquefied deposits in conjunction with topographic conditions which expose
or daylight the underlying weak soil deposits.
Figure C-3: Translational Failure
June 2014
4/15
APPENDIX C
C1.6 Piping Failure
Failures by piping can be developed from two different processes which can be categorized as subsurface
erosion induced or heave induced. Of the two types of piping conditions, subsurface erosion induced piping
failures are the principal failure mechanism with respect to dikes and/or dams. Under static conditions, piping
occurs when hydraulic gradients at or near the toe of a water compound exceeds unity (i.e. the change in total
head pressure head over a unit path length exceeds unity). Piping manifest as a local spring or discharge of
water containing suspended sediments. Over a prolonged period of time, internal erosion will progress towards
the water compound. When the internal erosion reaches the water compound, an “effective” pipe condition is
generated which can substantially increase the flow and erosion process, quickly leading to eventual collapse of
the foundation deposits and the dike/dam supported by the foundation deposits.
During seismic shaking, tension cracks can develop within the dike due to differential distortions along the
facility. In the instances where the tension cracks extend through the full cross section of the dike, an effective
“pipe” condition is developed which allows unobstructed flows to pass through the dike where retained water
levels are intercepted by the tension cracks. Similar to the static piping, flows through the dike can result is
significant or substantial erosion in a relatively short period of time, resulting in failure of the dike and loss of
water containment.
C1.7 Overtopping
Overtopping of the dike under seismic conditions can occur when there is a significant crest elevation decrease
as a result of liquefaction induced settlement and/ or slope failure occurring within the dike. Overtopping of the
dike can lead to a breach in the structure as a result of rapid erosion developing along the downstream face of
the dike. Overtopping of the dike can also occur as a result of a large wave passing over the dike (such as a
tsunami for sea dikes), or an effective dam created across a river course by a large landslide.
C2.0 MITIGATION METHODS FOR EARTHQUAKE INDUCED DIKE
FAILURES
Where the design and analyses of new or upgraded dikes indicate that conventional dike construction
methods/practices currently outlined by MFLNRO for static dike design will not meet with the seismic
performance criteria established for high consequence dikes, additional design measures will need to be
considered to improve the dike system to meet with the updated seismic design objectives. The extent of
additional dike improvements or mitigation methods required to meet with the seismic design objectives will be
dependent on the severity of the affects or impacts on the dikes by the selected seismic events. For example,
where the selected seismic ground motions results in predominantly vertical subsidence of the dike, a simple
raising of the dike to accommodate the estimated earthquake induced subsidence to maintain the desired free
board may be sufficient. However, where there is a potential for significant or substantial earthquake induced
combined horizontal and vertical deformations, such as a global slope failure within the dike, a combination of
several stability improvement approaches such as widening and raising the dike, flattening the slopes of the
dike, implementation of ground stabilization measures, etc. may be required. The feasibility of the various dike
improvement approaches to meet with seismic design requirements will be site specific and consequently,
cannot be generalized with a stipulated approach (i.e. the dike improvement solutions will be unique to meet with
the site specific conditions).
June 2014
5/15
APPENDIX C
It is recognized that some potential failure mechanisms can only be speculated (at best) and will be difficult to
confidently evaluate with respect to developing mitigation measures. Such mechanisms would include the
potential for a strike or thrust fault located below the dike, or determining the potential size and magnitude of a
seiche or tsunami wave that may impact a dike. In such instances, sound engineering judgment may provide the
only basis for reviewing these conditions.
The following presents various methods for improving dike stability to meet with the seismic performance criteria
as established by the MOE.
C2.1 Modifying the Existing Dike Profile
Where space permits, modification of the existing dike profile may provide sufficient stability to meet with the
objectives of the seismic performance criteria. Modification of the existing dike profile may include a combination
of the following:

Raising the dike;

Widening the dike; and/or,

Flattening the waterside and landside slopes.
The objective of modifying the dike profile is to reduce the potential for slope instability during and/or following
seismic shaking, or at least maintain sufficient free board to retain the water following a major earthquake. As a
minimum, the performance expectation of the post earthquake dike condition is that the dike can be reclaimed
within a relatively short period of time to accommodate a potential 10 year flood event.
In the event that spatial constraints and/or the extent of post earthquake deformations are excessive, other forms
of ground treatment to meet the seismic performance criteria should be considered, which may be implemented
in conjunction with the measures described above. The following discussion presents a review of ground
treatment alternatives that may be considered to improve seismic stability of a dike.
C2.2 Ground Improvement
The predominant failure mechanisms are deformations and/or displacements generated by liquefaction and/or
cyclic softening of the deposits within and/or beneath the dike. By mitigating the risk of liquefaction or cyclic
softening within and/or beneath the dike, substantial damage or failure of the dikes can be significantly reduced,
or at least sufficient stability will be provided to the dike that meets with expected performance criteria for the
design seismic hazard. Depending on the site-specific ground conditions and project-specific design
requirements, it may be feasible to limit the extent of ground improvement to specific areas and still reduce
deformations to within the performance criteria (as opposed to extensive densification of all potentially liquefiable
zones beneath and beyond the dike profile). There are several commonly used approaches for mitigating
liquefaction and they can be categorized according to their function as presented below:
June 2014
6/15
APPENDIX C

Densification or Strengthening – densification is a process used to describe the effective “tightening” of the
soil particles to increase the cyclic shear resistance of the deposits. Some examples of typical ground
densification methods are; vibro-compaction, displacement piling such as driven piles or compacted gravel
piles, vibro-replacement, explosive compaction, compaction grouting, rapid impact compaction and
dynamic compaction.

Drainage – Vertical drainage provides for dissipation of pore pressure during seismic shaking and
consequently, allows for volumetric decreases within loss of soil strengths. Examples of vertical drains
include wick drains, sand compaction piles and stone columns (depending on the surrounding deposits).

Inclusions – Depending on the type of failure mechanism under consideration, inclusions can be used to
reduce the risk of significant movements and/or the effect of piping failures caused by differential distortions
within the dike alignment. Examples of such inclusions are; sheet piles, secant piles, soil-cement mix
panels and jet-grout columns. Inclusions may also be used for reinforcement and containment of the
liquefied deposits by reducing the cyclic loading on the deposits and consequently, reducing the potential
for liquefaction.
The following presents a brief discussion of the various ground improvement techniques as described and
adopted from the 2007 Task Force Report for the Greater Vancouver Region, a public domain document. Cited
references are provided in the Task Force document.
C2.3 Densification or Strengthening
a)
Vibro-compaction and vibro-replacement are generally performed with electric or hydraulic powered
vibrators that are jetted into the ground with water or water/air mixture. In vibro-compaction, the natural
sand self-feeds into the void created by the vibro-flot, whereas in vibro-replacement crushed stone is used
as backfill. Top-feed and bottom-feed vibro-replacement methods are used. In the top-feed method, the
stone is introduced into the jetted hole from the ground surface, whereas in bottom feed the stone or gravel
is transmitted down the hole via a pipe and introduced at the bottom of the hole. Bottom feed is often
carried out using air jetting. The latter method allows the use of finer backfill material and potentially less
mixing of the native soil and stone occurs. Vibro-replacement is generally effective in soils containing less
than 15 to 20% fines (Martin et al, 1999). Luehring et aI, 1998 showed that non-plastic sandy silts can be
densified by a combination of vibro-replacement and vertical wick drains.
The equipment should be capable of delivering sufficient centrifugal force to cause the required
densification. Stone backfill materials should generally be clean and hard. Crushed stone should be used
when the stone backfill is to provide reinforcement for vertical or horizontal deformations. The depths of the
vibrator, stone usage, and amperage or power developed are often monitored during the work. Achievable
improvement depths are typically in the 25 to 35 m range although greater depths have been achieved with
special equipment. Vibro-replacement is the most widely used liquefaction countermeasure in Vancouver
and elsewhere in North America (Hayden and Baez 1994). Design information and equipment
characteristics can be found in many publications including Barksdale and Bachus (1983), Mitchell and
Huber (1985), Dobson (1987), Baez (1995 and 1997).
June 2014
7/15
APPENDIX C
b)
Dynamic compaction uses impact on the ground surface to densify subsurface soils. Weights typically
ranging from 10 tons to 30 tons are repeatedly lifted by a specially modified crane and dropped from about
15 m to 40 m heights. The amount of compaction and densification depth is a function of the weight, drop
height, number of drops per point and the spacing of the grid. Empirical relationships are available to
design deep dynamic compaction programs (Lukas 1986). Typically, treatment depths of up to
approximately 11 meters are achievable in granular soils. A granular pad is often placed if surficial
saturated cohesive soils are present or if the groundwater table is within 1 to 1.5 m of the surface. The
major limitations of the method are limitations on the depth of compaction that can be achieved and, if used
in an urban environment, vibrations, flying matter, noise, and perception of damage. For these latter
reasons, work often requires 30 to 60 m or more clearance from adjacent occupied buildings or other
sensitive structures.
Energy delivered to the ground, sequence spacing and timing of drops, as well as ground response in the
form of crater depth and heave of the surrounding ground are important quality control parameters. The
location of the water table and presence of surface "hard pans" can greatly affect the quality and outcome
of the densification process. Pore water pressure within recently treated areas should be allowed to
dissipate before secondary treatments are implemented.
c)
Rapid impact compaction (RIC) is analogous to dynamic compaction in that the ground surface is impacted
with a weight. The difference is that the weight and drop height are smaller and more frequent. In RIC, a
weight of approximately 7.5 tonne is dropped about 1.2 m to impact a 1.5 m diameter footing. A
pile-driving-like hydraulic hammer is used to lift and drop the weight at 40 to 60 blows per minute. Like
dynamic compaction the penetration depths are limited, however improvement depths greater than 6 m
have been achieved in ideal granular soils. The efficiency of RIC will diminish with finer materials. The
ability of RIC developing the required densification for significant ground motions associated with seismic
hazards with low return periods may also be limited or unachievable. The drop height, number of blows,
penetration per blow, and total energy per point are monitored by a data acquisition system. Vibrations
from the work will be similar to those from pile driving and must be considered if working near structures,
especially if they are occupied.
d)
Compaction grouting involves pumping low slump, mortar-type grout under pressure to density loose soils
by compaction. Effective treatment requires that the grout push the soil aside rather than fracture or
permeate it. Compaction grouting pipes are typically drilled-in or driven steel pipes of 50 mm internal
diameter or greater. Pressures ranging from 700 to 2100 kPa (100 to 300 psi) are used to inject a stiff,
75 mm or less slump, cement grout. In granular soil susceptible to liquefaction refusal pressures of 2800 to
3500 kPa (400 to 500 psi) are common (Martin et al. 1999). Grout pipes are typically installed in a grid
pattern of 1.5 to 3 m spacing. Often, primary spacing patterns with secondary or tertiary intermediate
patterns are used. Spacing and sequence of the grout points affects the quality of densification and ground
movements achieved.
Grouting volumes in granular soils typically range from 3 to 12 percent of the treated soil. However,
volumes up to 20 percent have been reported for extremely loose sands or silty soils. The procedure is not
effective when vertical confinement is less than 2.4 to 3 m of overburden (Martin et al. 1999). Information
on this technique can be found in Graf (1992), Baez and Henry (1993), Boulanger and Hayden (1995), and
Warner (2004).
June 2014
8/15
APPENDIX C
Slump, consistency of the mix, grout volumes, injection pressures, pore water pressures, and ground
movement at the surface, next to sensitive structures, and at depth are often monitored during the work.
Grout is typically injected in stages from the bottom up. At each stage a stopping criteria of grout volume,
pressure, or heave is followed before proceeding with the next stage. Grout casing should be at least
50 mm internal diameter to avoid high back pressures before sufficient grout is injected. Over-injection of
grout in a primary phase may result in ground heave and diminish densification effectiveness
(Martin et al, 1999).
e)
Compaction Piles- The driving of piles on close centers densifies the soil by pressure and vibration.
Pile shafts also have a reinforcing effect by acting as dowels between the soil layers. Timber and sand or
gravel compaction piles are commonly used. If the timber piles are permanently below the water table the
timber need not be treated. Piles are typically placed on 1.2 to 2 m centres and splices are sometimes
used to increase depth. Sand and gravel compaction piles are often made by vibrating in a pipe with an
expendable bottom plate. Upon extraction sand or gravel is introduced into the displaced void. Sand and
gravel compaction piles can also be constructed using expanded base pile procedures. The spacing of
sand and gravel compaction piles depends on pile diameter but is typically in the 1.2 to 2 m range.
Densification performance is often tested by carrying out penetration tests between the piles.
f)
Explosive compaction (EC) is carried out by setting off explosive charges in the ground. The principal
advantages of EC relative to other vibratory densification techniques is that it can be carried out to great
depth provided the soils are largely saturated. The method requires only drilling equipment and a supply of
explosives to implement. However, careful engineering design of the EC process is required to assure
reasonably uniform densification (through selection of the sequencing of the blast hole patterns) and
minimize offsite vibration effects (if required). The method is particularly cost effective where relatively
large volumes of soil are required to be densified at depths in excess of 6 m. The density of loose deposits
can typically be increased to relative densities in the range of 70 to 80% ((N1)60 of 20 to 25 and cone
penetration resistances (Qc1) of 100 to 130 bars).
Once an area of ground has been shot and pore pressures have largely dissipated, repeated applications
("passes") of shaking caused by controlled blast sequences causes additional settlement depending on soil
density and stiffness. The degree of densification obtainable will also depend on the fines content of the
sand as is the case for other methods of densification. The range of particle size for which blasting is
practical is the same as for vibro-compaction.
It has been observed that where blasting is used, there is a considerable time effect on the values of
penetration resistance. For the above reasons, initial evaluation of the effectiveness of the EC process is
based on direct measurement of soil volume change using in-situ settlement gauges.
C2.4 Drainage Measures
Passive drainage can be beneficial in both limiting the triggering of liquefaction and reducing the related
deformations. Seismic drains were proposed by the late Prof. Seed as a means of mitigation in the 1970's
(Seed & Booker 1977). Design procedures and the public domain program FEQDRAIN (Pestana et al. 1997)
are available. The intent of Seed's procedures was to prevent triggering of liquefaction.
June 2014
9/15
APPENDIX C
Recent research has shown that pore water migration and redistribution during earthquakes is important and
trapping of water under low permeability layers can lead to very weak interlayers or even a water film
(Kokusho 2003; Byrne et al. 2006). It is believed that this is the reason for the low residual strengths observed in
liquefaction case histories. For sites with low permeability barriers over liquefiable sand, drains can be used to
mitigate this effect and reduce ground deformations and potential for flow slide failure. Drains should also be
considered for reducing the pore pressure buildup within densified ground that is surrounded by liquefied soil,
especially where spatial constraints limit access for ground densification.
The performance of the drains is dependent on the following parameters:

Soil permeability;

Drain spacing;

Vertical flow capacity of the drain;

Soil density (capacity for volumetric compression);

Filter compatibility between the drain and native soil;

Elevation of point of discharge relative to water table; and

Rate of loading provided by the earthquake (i.e. if the earthquake liquefies the soil in one pulse the drains
will not have time to respond and temporary liquefaction may still occur, whereas if many pulses are
required to liquefy the soil then the drains may work well as the excess pore water is dissipated as it is
generated).
The use of drains without soil densification may not necessarily provide adequate pore pressure relief during the
period of strong earthquake shaking (unless the drains are on very close centers). However, they can have
beneficial effect in preventing flow slides and reducing lateral deformations
Drains can be constructed in several ways:

Pre-fabricated perforated pipe within a filter cloth sock -these can be installed in a drill hole or vibrated into
the ground using a mandrill;

Slotted pipe with surrounding filter sand or fine gravel installed in drill holes;

Traditional water wells with screen and filter;

Gravel or sand compaction piles;

Vibro-replacement columns constructed using filter sand and bottom-feed methods; and

Prefabricated wick drains.
June 2014
10/15
APPENDIX C
Shake table tests (Sasaki and Taniguchi, 1982) indicate that gravel drains can accelerate the dissipation of
excess pore water pressures, thereby limiting the loss of shear strength within the saturated deposits. Following
the 1993 Kushiro-Oki, Japan, earthquake, Iai et al. (1994a, 1994b) observed that quay walls having back fill
treated by the gravel drain pile and sand compaction pile techniques suffered no damage, while quay walls
having untreated backfill were severely damaged due to liquefaction. Seismic drains were tested at Massey
Tunnel by liquefying the soil with blasting.
The tests showed that both prefabricated drains with filter cloth sock and slotted pipe with surrounding filter sand
drains performed well. The tests also showed that large settlements may still occur in the vicinity of the drains,
and illustrated the importance of vertical flow capacity of the drain (large volumes of water have to flow over a
short period of time). However, the tests showed that liquefaction may still be triggered in the loose sand soils
located between the drains if they are subjected to high intensity short duration shocks (i.e. if pore pressures
build up in the soil significantly faster than it is dissipated by the drains).
C2.5 Inclusions
Inclusions within the dike may be considered where there is a significant risk of piping of the structure,
particularly if analyses indicate that the dike is at risk of producing continuous transverse cracks through the dike
(below the water level) as a result of significant differential horizontal or vertical displacements. Such conditions
may prevail where there is an abrupt change in the foundation deposits along the dike. The risk of piping failure
may be reduced by providing a relatively ductile, low permeability structure through the dike. Depending on the
magnitude of differential displacements the inclusion may comprise sheet piles, which is the most common
method used to establish a hydraulic cut-off. However, in some instances, the predicted strain or relative
displacement of the dike may be sufficient to yield or cause separation of the sheet piling. Other approaches for
mitigating the potential for post-earthquake hydraulic failure is to install a cut-off barrier comprising plastic
concrete that is capable of accommodating significant differential displacements while maintaining hydraulic
integrity of the cut-off barrier as well as maintaining a stiffness consistent or greater than the encapsulating dike
materials.
The inclusions may also be used to provide stability and reinforcement to the dike, similar to the methods
described for ground improvement and strengthening. In such cases, a mix of soil and cement are employed to
develop the stiffness and strength required to accommodate shear and bending stresses imposed by cyclic
shaking. Areas targeted for liquefaction mitigation may be stabilized by creating coherent cells which
encapsulate and confine the deposits and reduce the cyclic loading/pore pressure development within the cells.
The size and distribution of the cells are generally determined through rigorous analyses to review the effects of
distortions coupled with pore pressure generation within the cells.
Reinforcement cells may be created by jet grouting or soil-cement mixing methods. A brief discussion of each
method is presented below.
June 2014
11/15
APPENDIX C
Jet Grouting - The most common technique used in Jet Grouting involves the insertion of the Jet Grout Pipe to
design depth for the bottom of the soil-crete column. The pipe comprises a high strength drill rod with a hollow
center and special Jet Grouting Nozzles at the tip. The jetting pipe is advanced to the target depth using water
jets attached to the initial rod. Once the target depth has been reached, the rods are rotated slowly and
pressurized with grout slurry made typically of Portland cement and water.
High pressures (4000 - 6000 psi) are maintained to force the grout out laterally through special ports located in
the sides of the pipe, near the bottom. The slurry exits the jet port at very high velocity, impinges on the soil,
penetrating it several inches to feet away from the jets. The rotating jets destroy soft soil formations, and
uniformly mix the native soil with cement. Finally the rotating pipe is drawn slowly upward at a carefully
controlled rate so that the jets create an approximately cylindrical column of treated soil. The actual diameter of
the jet grout column is dependent specific items; soil conditions, grout mix, nozzle diameter, rotation speed,
withdrawal rate and grout pressure. Jet grout mixes are tailored to each project considering the soil type and the
application. Containment cell walls can be created by interconnecting (overlapping) two or more rows of jet
grout columns to achieve the desired wall thickness. The following figure presents a photograph of typical jet
grouting rig.
Figure C-4: Typical Jet Grouting Rig
Soil-Cement Mixing - Soil-mixing involves mixing cementitious materials with the native soil using a mechanical
mixing unit. Traditionally, soil mixing has been carried out using multiple hollow stem auger arrangement.
However, recent advances in the technology has produced a cutter soil mixer (CSM) specifically design to
generate homogenously mixed columns of soil-cement mixtures. The CSM differs from the traditional auger
technique where soil-cement mixtures are created with rotating cutter heads about a vertical axis. Cement, fly
ash, quicklime, and other additives are typically used in the grout to blend with the indigenous soils. Figures 5
and 6 present photographs of the two equipment types.
June 2014
12/15
APPENDIX C
Soil mix column depths of 30 m or more can be achieve with the equipment described above. Typically, the
liquefiable soil is contained within soil-mixed walls created by overlapping the soil mix inclusions. The procedure
reduces shear strain within the soil to reduce the potential for liquefaction and confines soils that do liquefy to
limit displacement. The walls also add shear strength to the overall soil-wall system. Column shear strengths of
1 MPa or more can be achieved, even in silty soils. The method has been used at Jackson Lake dam in
Wyoming (Ryan and Jasperse, 1989), which comprised honeycomb shaped cells placed at the heel and toe of
the dam. Other applications have included construction of underground barriers to circumvent significant lateral
displacements in liquefied or cyclically softened deposits. Columns are usually tested using wet sampling,
coring, CPT, pressuremeter, or seismic methods. Some variation in uniformity and strength should be expected.
Figure C-5: Typical Soil-Mix Auger Rig
June 2014
Figure C-6: Typical Soil Cutter Mix Rig
13/15
APPENDIX C
References
Baez, 1.1., 1997. Vibro-Stone Columns, Soil Improvement -A 20 Year Update, Ground Improvement, Ground
Reinforcement, Ground Treatment Developments 19871997, V.R. Schaefer (Editor), Geotechnical
Special Publication No. 69, ASCE, Logan, UT. 1997.
Baez, 1.1., and Henry, J.F., 1993. Reduction of Liquefaction Potential by Compaction Grouting at Pinoplis Dam,
SC, Proceedings of the Geotechnical Practice in Dam Rehabiliation Conference, ASCE Geotechnical
Special Publication No. 35, p. 493506, Raleigh, N.C.
Barksdale, R. D. and Bachus, R.C., 1983. Design and Construction of Stone Columns, Vol. 1., Report No. FHW
AlRD 83/026, Federal Highway Administration, 210 p.
Boulanger, R.W., and Hayden, R.F., 1995. Aspects of Compaction Grouting of Liquefiable Soil, Journal of
Geotechnical Engineering, ASCE, 121(12): 844-855.
Byrne, P.M., Naesgaard, E., and Seid-Karbasi, M., 2006. Analysis and design of earth structures to resist
seismic soil liquefaction, 59th Canadian Geotechnical Conference, Canadian Geotechnical Society,
Vancouver, B.C., October.
Dobson, T., 1987. Case Histories of the Vibro Systems to Minimize the Risk of Liquefaction, Soil Improvement-A
Ten Year Update, ASCE Symposium, J.P. Welsh, editor, Geotechnical Special Publication No. 12,
Atlantic City, p.167-183.
Graf, E.D. 1992. Compaction Grout, 1992, Grouting, Soil Improvement and Geosynthetics, ASCE Geotechnical
Special Publication No. 30, 275-287.
Hayden, R.F., and Baez , 1.1., 1994. State of Practice for Liquefaction Mitigation in North America, Proceedings
of the 4th U.S.-Japan Work shop on Soil Liquefaction, Remedial Treatment of Potentially Liquefiable
Soils, PWRI, Tsukuba City, Japan, July-4-6.
Kokusho, T., 2003. Current state of research on flow failure considering void redistribution in liquefied deposits.
J., Soil Dynamic and Earthquake Engineering, 23: 585-603.
Luehring, R., Dewey, B., Mejia, L., Stevens, M. and Baez, J. 1998. Liquefaction Mitigation of Silty Dam
Foundation Using Vibro-Stone Columns and Drainage Wicks -A Test Section Case History at Salmon
Lake Dam, Proceedings of the 1998 Annual Conference Association of State Dam Safety Officials,
Las Vegas, NV, October I 1-14.
Lukas, RG., 1986. Dynamic Compaction for Highway Construction, Volume I : Design and Construction
Guidelines, Federal Highway Administration Report No. FHWAlRD-86/133.
Martin, G.R. Lew, M.,. Arulmoli, K., Baez, 1.1., Blake, T.F., Earnest, 1., Gharib, F., Goldhammer, J., Hsu, D.,
Kupferman S., O'Tousa, 1. Real C.R., Reeder, W. Simantob E., and Youd, T.L., 1999. Recommended
procedures for implementation of DMG Special Publication 117 Guidelines for Analyzing and
mitigating Liquefaction hazards in California., G.R. Martin & M. Lew co-chairs, Southern California
Earthquake Center, University of Southern California.
June 2014
14/15
APPENDIX C
Mitchell, J.K., and Huber, T.R., 1985. Perfonnance of a Stone Column Foundation, Journal of Geotechnical
Engineering, ASCE, 111(2): 205-223.
Pestana, lM., Hunt, C.E. and Goughnour, R.R. 1997. FEQDrain: A Finite Element Computer Program for the
Analysis of the Earthquake Generation and Dissipation of Pore Water Pressure in Layered Sand
Deposits with Vertical Drains, Report No. UCBIEERC-97-15, December 1997.
Ryan, C.R., and Jasperse, B.H. 1989. Deep Soil Mixing at the Jackson Lake Dam, Foundation Engineering:
Current Principles and Practices, Proceedings of an ASCE Congress, Geotechnical Special
Publication No. 22, Vol. 1, p. 354-367.
Sasaki, Y., and Taniguchi, E. 1982. Shaking Table Tests on Gravel Drains to Prevent Liquefaction of Sand
Deposits, Soils and Foundations, Japanese Society of Soil Mechanics and Foundation Engineering,
22(3): 1-14.
Seed, H.B. & Booker, J.R. 1977. Stabilization of Potentially Liquefiable Sand Deposits Using Gravel Drains,
Journal of the Geotechnical Engineering Division, ASCE, New York, NY, 103(GT7): 757-768.
Warner, J. 2004. Practical Handbook of Grouting -Soil, Rock, Structures, John Wiley & Sons, Inc., Hoboken, NJ,
720 p.
o:\final\2010\1447\10-1447-0333 (seismic)\1014470333-003-r-rev2\component\appendix c - final draft.docx
June 2014
15/15
APPENDIX D
Remediation of Seismic Damage to Dikes
APPENDIX D
D1.0 INTRODUCTION
Dike geometry and construction vary considerably throughout the Fraser floodplain. The dikes were originally
constructed many decades ago using less sophisticated construction techniques and with less quality control
than present day earthworks construction. Dike upgrade works over the last 40 years or so used engineering
principles and better material and construction control to develop robust and safe structures. However,
economics sometimes dictated the degree of safety and inherent design criteria adopted. Regardless, the
geometric standard for dike construction throughout the Fraser floodplain has generally been implemented and
most dike slopes conform to the Dike Design and Construction Guide, Best Management Practices for
British Columbia published in 2003 by the Ministry of Environment (formerly, Ministry of Water, Land and
Air Protection). This therefore, somewhat simplifies the repair procedures as geometric conformity exists.
D1.1 Dike Breach
A breach in a dike can be initiated as a result of applied dynamic forces from earthquakes, which are associated
with the forces of the water being retained, forces on the body of the dike, and weaknesses in the body of the
dike and the underlying foundation soils. The common dike breach mechanisms are as follows:

Overtopping: Riverine flooding, tsunami, and wave run-up results in overtopping of the crest of the dike
whereby the overtopping flow finds a low depression and weak spot in the dike which initiates localized
erosion and down-cutting of the dike fill. The erosion continues and accelerates due to concentration of
flow which can then lead to a breach in the dike. Overtopping could also occur from complete loss of
freeboard due to lateral spreading of the dike structure by earthquake-induced liquefaction of the foundation
soils beneath and adjacent to the dike.

Piping (Internal Erosion) / Seepage: Piping is a result of uncontrolled seepage either through the
structure of the dike or through the underlying foundation soils. The seepage can occur post-earthquake
due to cracking of the dike fill materials or liquefaction-induced movements. These discontinuities (cracks
and localized openings) can concentrate seepage and result in piping (internal erosion or loss of soil) and
the formation of “sand boils” which eject water and sediments. Uncontrolled piping can propagate into
preferred seepage flow paths that develop within and beneath the dike which results in hydraulic
connection to the water side and progressive failure and breach of the dike.

Sliding/Foundation Soil Failure: Movement, cracking or failure of the dike, or portions of the dike, that
occur as a result of the lateral force(s) transmitted to the dike structure that exceeds the reduced shear
resistance of the dike fills and underlying foundation soils (caused by soil liquefaction during earthquake
shaking).
June 2014
1/4
APPENDIX D
D1.2 Dike Remediation
D1.2.1
Temporary Emergency Repairs
The inspection guidelines for flood control dikes after an earthquake event are outlined in Appendix B. In the
event that there is evidence of a breach or a developing breach from any of the above mechanisms, emergency
repairs will likely need to be initiated. The degree to which such work will be required depends on the urgency
dictated by the water level behind the dike at the time of the breach. Dike emergency (temporary) repair
techniques include:

Infilling by placing and compacting suitable fill into the breach to fill the hole in the system. This is
somewhat time consuming and will depend on the availability of fill and truck and equipment access to the
breach location. The infilling can temporarily plug the hole in the dike but further review, analysis and
design will be required to remediate the dike once the flood threat has passed;

Sand-bagging is a commonly used method for raising dikes crests or filling voids when emergency
conditions dictate. Sand bags can also be used to prevent piping from boils by constructing a sand bag
ring around the boils. This technique restricts flow and velocity which prevents soil loss; and

Water Filled Fabric Tubes (Aqua dam, rubber inflatable dam). The use of inflatable fabric /rubber tubes to
fill breaches in dikes has been investigated. The photographs shown on Figures D-1 and D-2 are
reproduced from Resio et al (2008) and show the effectiveness of this repair in filling a breach and stopping
uncontrolled flow. The tubes can be transported quickly and easily to the breach location and filled with
water using a small pump system. The use of such tubes/bags also allows the freeboard of any dike
system to be quickly raised.
Figure D-1: Sample deployment of deep-breach closure system, with a small residual flow still persisting along the upper
edges of the breach opening (Resio et al, 2008).
June 2014
2/4
APPENDIX D
Figure D-2: Parallel flow concept Resio et al, 2008).
D1.2.2
Permanent Remediation of Damaged or Failed Dike Sections
After an earthquake event (and after the flood threat has passed, where both of these events occurred
concurrently), a detailed inspection of the damaged section(s) of dike will need to be carried out to assess the
extent of damage and the likely mechanism(s) of future failure. The type of remediation required will be a
function of the level of damage that has occurred to the dike. Some likely damage scenarios and options for
remediation of damage or failed dike sections are outlined below.
D1.2.2.1
Remediation of Localized Small Scale Damage
Localized sloughing and slumping, where the overall integrity of the dike has not been compromised, can in most
instances be repaired by means of regrading and addition of some fill. It may be possible to seal localized
tension cracks using bentonitic grout.
D1.2.2.2
Remediation of Dike Failures
In areas where the dike has failed (i.e. loss of freeboard, side slope failure, lateral movement of the dike and the
like) where the remaining dike structure in the affected area is no longer capable of serving its intended purpose,
complete re-construction should be carried out. If the dike failure(s) has occurred as a result of seismic
liquefaction, then consideration should be given to densification of the ground adjacent to the toe(s) of the dike
and possibly beneath the dike in severe circumstances. Details on densification techniques commonly used are
outlined in Appendix C. Detailed analysis should be carried out to determine:

The extent of densification (i.e. width of zone to be densified beyond the toe of the dike) that is required.
Property considerations (i.e. proximity of neighbouring structures, limited property width or Right-of-Way
etc.) may in some instances dictate whether or not densification is feasible;

fill requirements for reconstruction in areas where dike failure has occurred from piping; and

Filter compatibility between the various materials used to re-construct the dike to minimize the potential for
future piping.
June 2014
3/4
APPENDIX D
D1.2.2.3
Sand Boils
Where sand boils and/or piping failures are identified beyond the land side toe of the dike, drains may be
installed to promote controlled release of hydraulic pressures during future seismic and/or flood events.
Alternatively, a filtered berm can also be installed to reduce the potential for future boils and/or piping failures.
Filter compatibility will be key to the successful operation of these remedial measures
D1.2.2.4
Appurtenant Structures
In areas where relative deformation has occurred between a more rigid structure (i.e., a pumphouse or floodbox)
and the adjacent more flexible earthen dike structure, site-specific investigations (Geophysics or possibly
probing) should be carried out to try to identify if voids or zone of loosened soil have developed in the
surrounding areas adjacent to the structure. If voids are detected, then injection grouting (using bentonitic grout)
may be used to fill these voids or alternatively, localized reconstruction may be required to repair the dike.
Damage that has occurred to pumphouses, floodboxes and the like should be addressed by a qualified structural
engineer.
REFERENCES
Resio, D., Boc, S., Maynord,S., Ward,D., Abraham, D., Dudeck, D., Welsh,B, (2008), Development and
Demonstration of Rapid Repair of Levee Breaching Technology, Coastal and Hydraulics Laboratory,
Engineering research and Development Control;, Vicksburg, USA
o:\final\2010\1447\10-1447-0333 (seismic)\1014470333-003-r-rev2\component\appendix d - final draft.docx
June 2014
4/4
APPENDIX E
Report Format/Table of Contents
Seismic Design and Analysis Requirements for
Dikes
APPENDIX E
Design and Analysis Requirements for High Consequence Dikes
REPORT FORMAT/TABLE OF CONTENTS
DESIGN AND ANALYSIS REQUIREMENTS FOR HIGH CONSEQUENCE DIKES
The following outline summarizes the reporting requirements for seismic design and evaluation of
High Consequence Dikes for site-specific seismic studies. For consistency of review by the Flood Safety
Section, the following is suggested.
A.
1.
2.
3.
4.
5.
6.
7.
8.
Summary of Dike, Soil and Water Level Data
Plan Location of Dike and UTM Coordinates
Dike Segment Identification and Type of Dike (River, Sea Dike, etc.)
Dike Configuration
Applicable Appurtenant Structures
Dike and Foundation Soil Conditions
Mean annual water level and 1:10 yr water level
Surrounding Dike Identification(s) and Specific Site Features
Impacted Community (Farm, Urban, etc.)
B.
1.
2.
Site-Specific Seismic Hazard
Plate Tectonic Environment
Site-Specific PGAs and Uniform Hazard Spectra (from GSC Interactive Website) for Site Class C for
EQL1, EQL2, and EQL3
Site Class as per 2010 NBCC or 2012 BCBC
Fa Value as per 2010 NBCC or 2012 BCBC
Time-Histories of Accelerations for EQL-1, EQL-2 and EQL-3 Used in the Design
Where Optimization of Deformations is Undertaken
[Mean response values to be considered when using 7 or more time-histories.
Maximum response values to be considered when using 3 time histories].
3.
4.
5.
C.
1.
2.
3.
Results of Field and Laboratory Investigations
Field Investigation Program and Methods Used
Laboratory Testing Program and Standards Used
Geotechnical/Geological Model Developed for the Site
D.
1.
2.
Dike and Foundation Soil Characterization
Material Zones, Strength, and Stiffness Characteristics
Summary of Parameters – Static Stability Analysis
[Fines Corrected SPT N60 or Qt Profiles or Values, angle of internal friction, cohesion, total and
submerged unit weights]
Summary of Parameters – Seismic Stability Analysis
[Fines Corrected SPT N60 or Qt Profiles or Values, Maximum Shear Moduli and Damping Ratio Profiles,
Total unit weight of geological material zones, Peak Undrained Shear Strength and Post-Liquefaction
Residual Shear Strength of Soils, Hydraulic Conductivity Values, Estimated Overconsolidation Stress]
3.
June 2014
1/2
APPENDIX E
Design and Analysis Requirements for High Consequence Dikes
E.
1.
2.
3.
4.
5.
Analysis Methodology
Summary of Analysis Procedures for Static and Seismic Stability
Summary of Analysis Procedures for Seismic Deformations
Summary of Analysis Procedures for Seepage
Computer Software Programs
Analysis Assumptions
F.
1.
2.
3.
4.
5.
6.
Results of Dike Analyses
Slope stability – Static and Seismic
Liquefaction Potential
Settlement Potential
Seepage
Defensive Design Measures
Deformation Analyses
G.
1.
2.
3.
4.
Results of Foundation Analyses – Appurtenant Structures
Liquefaction Potential
Bearing Capacity
Settlement and Deformation Analyses
Defensive Design Measures
June 2014
2/2
APPENDIX F
Example Problem – Dike Seismic Stability
APPENDIX F
Example Problem
1.0
PREAMBLE
An example problem for dike seismic stability analysis has been formulated to illustrate the concepts, methods
of analyses, and procedures described in this guideline. The example problem does not include seepage and
site-specific wave propagation analyses.
If the river water levels required for the analyses are not provided by or available from the local government or
the Flood Safety Section, consultants are to undertaken analyses to establish the required data.
2.0
DESCRIPTION OF THE DIKE
The dike considered in this example problem is located near a river bank. Figure 1 shows the dike location and
Figure 2 shows a cross section of the dike. Material properties considered in the slope stability analyses are
summarized in Figure 2. The existing dike extends to Elevation +4.7 m, has a gravel road that is approximately
4.5 m wide, and has landside and waterside slopes of 3H: 1V.
3.0
AVAILABLE INFORMATION (SECTION 11)
Item
No.
Details of Information
Yes/No
Reference
1
Dike Location
Yes
Figure 1
2
Dike cross section
Yes
Figure 2
3
Dike Classification
Yes
High Consequence
4
Type of Dike
Yes
River
5
Appurtenant structures
No
-
6
Surficial geology data
Yes
GSC Map 1484A
7
Bathymetry Data
No
8
Geotechnical Report
Yes
From Available River
Bathymetry Survey
Golder (2001)
9
Dike inspection report(s)
No
-
10
Mean river water level/sea level
Yes
+0.5 m (Geodetic El.)
See MOE Map
11
1:10 yr Water Level
Yes
+0.4 m (Geodetic El.)
12
Conventional Dike/Super Dike/Other
-
N/A
June 2014
1/6
APPENDIX F
Example Problem
4.0
GROUND MOTION PARAMETERS (SECTION 11)
Site coordinates:
Latitude (N), Longitude (W)
Site Class C Ground Motion Parameters (cf. NBCC 2010 Interactive Website):
Return Period
PGA (g)
Sa(0.2s)
Sa(1.0s)
1:100-yr
0.12 g
0.24 g
0.08 g
1:475-yr
0.27 g
0.53 g
0.17 g
1:2,475-yr
0.50 g
1.01 g
0.34 g
Earthquake Magnitude for Liquefaction Analysis (Section 13 of the Guidelines Document):

Mw 6 for EQL-1

Mw 7 for EQL-2 and EQL-3
Site Classification:
Class D (NBCC 2010, Table 4.1.8.4A)
Dike Apex Angle:
163 degrees (Refer to Figure 3 for illustration)
Apex angle amplification factor
EQL-1:
= (180/163)
= 1.1
Sa(0.2 s) = 0.24 g
Fa = 1.3 (NBCC 2010, Table 4.1.8.4B, also Table 3 of the Guidelines Document)
PGA_Max
= 0.12 x 1.3
= 0.16 g
PGA_Min
= 0.12 x 1.3 x 0.80
= 0.13 g
Design PGA
= 0.13 x 1.1
= 0.14 g: EQL-1 Includes topographic effects
[Note: If site-specific 1D ground response analyses indicate higher PGA than PGA_Min, use the
computed PGA as the Design PGA]
EQL-2:
Sa(0.2 s) = 0.53 g
Fa = 1.2 (NBCC 2010, Table 4.1.8.4B, Also Table 3 of the Guidelines Document)
PGA_Max
= 0.27 x 1.2
= 0.32 g
PGA_Min
= 0.27 x 1.2 x 0.60
= 0.19 g
Design PGA
= 0.19 x 1.1 g
= 0.21 g: EQL-2 Includes topographic effects
June 2014
2/6
APPENDIX F
Example Problem
EQL-3:
Sa(0.2 s) = 1.01 g
Fa = 1.1 (NBCC 2010, Table 4.1.8.4B)
PGA_Max
= 0.50 x 1.1
= 0.55 g
PGA_Min
= 0.50 x 1.1 x 0.50
= 0.28 g
Design PGA
= 0.28 x 1.1 g
= 0.31 g: EQL-3, Includes topographic effects
5.0
LIQUEFACTION INDEX CALCULATION
Results based on Seed’s Simplified Analysis, C = 0.65 , Mean Shear Stress Reduction Coefficient; rd. (Refer to
Figure 4 for liquefaction assessment)
EQL-1:
Liquefaction Index
= L0
EQL-2:
Liquefaction Index
= L2
EQL-3:
Liquefaction Index
= L3
6.0
EQL-1:
PSEUDO-STATIC ANALYSIS
Liquefaction index
= L0
Seismic Coefficient
= PGA
= 0.14; no liquefaction
FOS_Slip Surface 1
= 1.5
FOS_Slip Surface 2
= 1.8
FOS_Slip Surface 3
= 1.8
(Refer to Figure 5 for typical slip surfaces that can affect the integrity of the dike body)
FOS > 1
Displacement calculations are NOT required.
Settlement calculations are NOT required.
Meets freeboard requirement (i.e. ≥ 0.3 m, > 1:10 yr flood level)
Design satisfies EQL-1.
EQL-2:
Liquefaction Index
Seismic coefficient for flow slide failure
Seismic coefficient for displacement calculations
June 2014
3/6
= L2
= 0.0
= ½ PGA = 0.11
APPENDIX F
Example Problem
Stability
FOS_Flow Slide Failure = 1.02 > 1.0 (See Figure 6 for stability analysis on flow slide)
(qc1N-CS = 120, Residual shear strength ratio = 0.16 with void redistribution curve is used for
assessment of residual shear strength ratio)
Displacements
2
FOS_Slip Surface
= 1.0 (Ky = N = 0.02 g, Simplified Newmark Displacement = 6 V /2gN =
0.7 m for N/A < 0.2, and normalized acceleration to velocity ratio A/V ≈1, for Fraser Lower
Mainland Only)
(See Figure 7 for yield acceleration assessment)
Maximum Horizontal Displacement=
0.7 m > 0.3 m
Performance criteria are not satisfied.
Modification of configuration or ground improvement is necessary.
7.0
MODIFIED CONFIGURATION – PSEUDO STATIC ANALYSIS
Flatten Waterside Slope (Waterside slope is flattened to 5H:1V – See Figure 8 for previous and new
configuration)
Revised dike apex angle: 169 degrees
Apex angle amplification factor
Calculate new design PGAs:
EQL-1:
Design PGA
EQL-2:
Design PGA
EQL-3:
Design PGA
EQL-1:
= (180/169)
= 1.1
= 0.13 x 1.07
= 0.19 x 1.07
= 0.28 x 1.07
= 0.14 g: EQL-1 Includes topographic effect,
= 0.20 g: EQL-2 includes topographic effects
= 0.30 g: EQL-3, Includes topographic effects
Liquefaction index
= L0
(CSR profiles are changed with the alteration in PGA. Refer Figure 9 for new liquefaction
assessment)
Seismic Coefficient
= PGA
= 0.14 ; no liquefaction
FOS_Slip Surface 1
= 1.8
FOS_Slip Surface 2
= 1.8
FOS_Slip Surface 3
= 2.1
FOS > 1
Displacement calculations are NOT required.
Settlement calculations are NOT required.
Meets freeboard (i.e. ≥ 0.3 m, > 1:10 yr flood level)
June 2014
4/6
APPENDIX F
Example Problem
EQL-2:
Liquefaction Index
= L2
= 0.0
= ½ PGA = 0.10
Stability
FOS_Flow Slide Failure = 1.12 > 1.0
(qc1N-CS = 120, Residual shear strength ratio = 0.16 with void redistribution curve is used for
assessment of residual shear strength ratio)
Displacements
FOS_Slip Surface 1
= 1.000 (Ky = N = 0.05 and Simplified Newmark Displacement = 6
2
V /2gN = 0.2 m for N/A < 0.2, and normalized acceleration to velocity ratio A/V≈1, for Fraser
Lower Mainland Only)
Maximum Horizontal Displacement
=
0.2m < 0.3 m
Vertical Settlement (Ref. Figure 7b and CPT Data)
=
0.1 m < 0.15 m
(Vertical settlement calculated from CSR = 0.16 and volumetric strain = 0.75%)
Meets freeboard (i.e. ≥ 0.3 m, > 1:10 yr flood level)
EQL-3:
Liquefaction Index
Stability
FOS_Flow Slide Failure = 1.1 > 1.0
Displacements
= L3
= 0.0
= ½ PGA = 0.15
2
FOS_Slip Surface 3
= 1.0 (Ky = N = 0.05 and Displacement = 6 V /2gN = 0.6 m for N/A <
0.2, and normalized acceleration to velocity ratio A/V≈1, for Fraser Lower Mainland Only)
Maximum Horizontal Displacement
=
0.6 m < 0.9 m
Vertical Settlement Vertical Settlement (Ref. Figure 7b and CPT Data) = 0.4 m < 0.5 m
(Vertical settlement calculated from CSR = 0.24 and volumetric strain = 2.35%)
Design satisfies freeboard requirement (i.e. ≥ 0.3 m, > 1:10 yr. flood level).
NOTE: Design is satisfied with the improved slope on waterside of the dike. However designer
may have elected to go with ground improvement as an alternative, if dike setback on landside
is not possible. In such a case, start with the original configuration of the dike.
Design Complete. No more iterations are required.
June 2014
5/6
APPENDIX F
Example Problem
8.0
SIGNOFF
ABC, P. Eng.
----------------------------------------------------Designer
XYZ, P. Eng.
-----------------------------------------Reviewer
Date: 12 November 2013
June 2014
6/6
Dike
PROJECT
SEISMIC DESIGN GUIDELINESS FOR DIKES
MINISTRY OF FORESTS, LANDS AND NATURAL
RESOURCE OPERATIONS - FLOOD SAFETY SECTION
TITLE
DIKE SEISMIC STABILITY EXAMPLE –
TYPICAL DIKE LOCATIONS
PROJECT No. 12-1447-0119 PHASE No. 1000
DESIGN
06NOV13 SCALE NTS
AT
---CADD
06NOV13
06NOV13
CHECK UDA
REVIEW
REV.
FIGURE 1
UDA
06NOV13
PROJECT
TITLE
DIKE CROSS SECTION
DESIGN AT
06NOV13 SCALE NTS
---CADD
06NOV13
CHECK
UDA
06NOV13
REVIEW UDA
06NOV13
REV.
FIGURE 2
Apex Angle (= 163°)
3H
1V
PROJECT
TITLE
APEX ANGLE SELECTION
DESIGN AT
06NOV13 SCALE NTS
---CADD
06NOV13
CHECK
UDA
06NOV13
REVIEW UDA
06NOV13
REV.
FIGURE 3
Comparison of CSR-SSMA vs CRR for EQL2
0
0.05
0.1
0.15
CSR
0.2
0.25
0.3
0.35
0
0.4
0.05
0.1
0.15
CSR
0.2
0.25
0.3
0.35
0.4
0
0
0
0.05
0.1
0.15
CSR
0.2
0.25
0.3
0.35
0.4
0
CRR CPT12-01
CRR CPT12-01
CRR CPT12-02
CRR CPT12-01
CRR CPT12-03
CRR CPT12-02
CSR-SSMA
CRR CPT12-03
CRR CPT12-02
CRR CPT12-03
CSR-SSMA
CSR-SSMA
5
10
10
10
Depth (m)
Depth (m)
5
Depth (m)
5
15
15
15
20
20
20
25
25
25
PROJECT
TITLE
LIQUEFACTION ASSESSMENT
DESIGN
06NOV13 SCALE NTS
AT
CADD
-06NOV13
CHECK
UDA
06NOV13
REVIEW
UDA
06NOV13
REV.
FIGURE 4
PROJECT
TITLE
SLIP SURFACES CONSIDERING DIKE FAILURE
DESIGN AT
06NOV13 SCALE NTS
---CADD
06NOV13
CHECK
UDA
06NOV13
REVIEW UDA
06NOV13
REV.
FIGURE 5
Liquefiable Sand Layer
PROJECT
TITLE
NO FLOW SLIDE FAILURE
DESIGN AT
06NOV13 SCALE NTS
---CADD
06NOV13
CHECK
UDA
06NOV13
REVIEW UDA
06NOV13
REV.
FIGURE 6
Yield Acceleration = 0.02 g
Liquefiable Sand Layer
PROJECT
TITLE
TYPICAL SLIP SURFACE ON DISPLACEMENT
CALCULATION
DESIGN AT
06NOV13 SCALE NTS
---CADD
06NOV13
CHECK
UDA
06NOV13
REVIEW UDA
06NOV13
REV.
FIGURE 7
3H:1V Slope
5H:1V Slope
PROJECT
TITLE
PREVIOUS AND PROPOSED DIKE
CROSS SECTIONS
DESIGN AT
06NOV13 SCALE NTS
---CADD
06NOV13
CHECK
UDA
06NOV13
REVIEW UDA
06NOV13
REV.
FIGURE 8
0
0.05
0.1
0.15
CSR
0.2
0.25
0.3
0.35
0
0.4
0
0
0.05
0.1
0.15
CSR
0.2
0.25
0.3
0.35
0.4
0
0.1
0.15
CSR
0.2
0.25
0.3
0.35
0.4
0
CRR CPT12-01
CRR CPT12-01
CRR CPT12-02
CRR CPT12-02
CRR CPT12-02
CRR CPT12-03
CRR CPT12-03
CRR CPT12-03
CSR-SSMA
CSR-SSMA
CSR-SSMA
CRR CPT12-01
5
5
10
10
10
Depth (m)
Depth (m)
5
Depth (m)
0.05
15
15
15
20
20
20
25
25
25
PROJECT
TITLE
LIQUEFACTION ASSESSMENT
FOR NEW PGSA
DESIGN
06NOV13 SCALE NTS
AT
CADD
-06NOV13
CHECK
UDA
06NOV13
REVIEW
UDA
06NOV13
REV.
FIGURE 9

Seismic Design Guidelines for Dikes - 2nd Edition

Transcription

Similar documents

Building with Nature

Melihat bencana dari kacamata anak yang lucu (gambar kacamata

Hydrocarbon Opportunities in Peru

NEW SOLUTION

Forecasting seismic risk as an earthquake sequence happens

IGSC7 Conference Book

New features of REXEL 2.61 beta, a tool for

Annemarie Ott Weist, Öznur Saygı-Arslan and Mark Roberts, Air

Purple Diamond® Semi

“Mark Ricciuto”